diff --git a/pkg/calc/solve.go b/pkg/calc/solve.go
index 44b5f57..df6abdc 100644
--- a/pkg/calc/solve.go
+++ b/pkg/calc/solve.go
@@ -22,12 +22,25 @@ func WeaponsForAttack(targetAttack, weaponsTech float64) (float64, bool) {
 // DriveForSpeed returns the drive block that yields targetSpeed for a
 // ship whose mass excluding the drive block is restMass, at drive tech
 // level driveTech, inverting [Speed] composed with [DriveEffective].
-// Speed approaches but never reaches the stripped-hull ceiling
-// 20*driveTech, so a target at or above the ceiling (or a non-positive
-// target or tech level) is infeasible.
+// With a positive restMass the speed approaches but never reaches the
+// stripped-hull ceiling 20*driveTech, so a target at or above the
+// ceiling is infeasible. With restMass==0 the drive block carries no
+// other mass: every positive drive yields exactly the ceiling speed, so
+// the ceiling target is the only feasible one and any positive drive
+// (canonically 1) solves it. Non-positive targetSpeed or driveTech are
+// always infeasible.
 func DriveForSpeed(targetSpeed, driveTech, restMass float64) (float64, bool) {
+	if driveTech <= 0 || targetSpeed <= 0 {
+		return 0, false
+	}
 	ceiling := 20 * driveTech
-	if driveTech <= 0 || targetSpeed <= 0 || targetSpeed >= ceiling {
+	if restMass <= 0 {
+		if targetSpeed != ceiling {
+			return 0, false
+		}
+		return 1, true
+	}
+	if targetSpeed >= ceiling {
 		return 0, false
 	}
 	return targetSpeed * restMass / (ceiling - targetSpeed), true
diff --git a/pkg/calc/solve_test.go b/pkg/calc/solve_test.go
index a032fce..bb7862c 100644
--- a/pkg/calc/solve_test.go
+++ b/pkg/calc/solve_test.go
@@ -24,12 +24,30 @@ func TestDriveForSpeed(t *testing.T) {
 	if !ok || math.Abs(got-drive) > 1e-9 {
 		t.Errorf("DriveForSpeed round-trip = %v (ok=%v), want %v", got, ok, drive)
 	}
-	// Speed can never reach the stripped-hull ceiling 20*driveTech.
+	// With a positive restMass speed can never reach 20*driveTech.
 	if _, ok := calc.DriveForSpeed(20*driveTech, driveTech, restMass); ok {
 		t.Error("DriveForSpeed at the speed ceiling should be infeasible")
 	}
 }
 
+func TestDriveForSpeedZeroRest(t *testing.T) {
+	// With restMass==0 the only achievable speed is the stripped-hull
+	// ceiling 20*driveTech; any positive drive reaches it. Off-ceiling
+	// targets are infeasible.
+	const driveTech = 1.5
+	ceiling := 20 * driveTech
+	got, ok := calc.DriveForSpeed(ceiling, driveTech, 0)
+	if !ok || got <= 0 {
+		t.Errorf("DriveForSpeed(ceiling, _, 0) = %v (ok=%v), want positive", got, ok)
+	}
+	if _, ok := calc.DriveForSpeed(ceiling/2, driveTech, 0); ok {
+		t.Error("DriveForSpeed(below ceiling, _, 0) should be infeasible")
+	}
+	if _, ok := calc.DriveForSpeed(ceiling+1, driveTech, 0); ok {
+		t.Error("DriveForSpeed(above ceiling, _, 0) should be infeasible")
+	}
+}
+
 func TestShieldsForDefence(t *testing.T) {
 	const shields, shieldsTech, restMass = 5.75, 1.0, 40.0
 	defence := calc.EffectiveDefence(shields, shieldsTech, shields+restMass)
diff --git a/ui/docs/calculator-ux.md b/ui/docs/calculator-ux.md
index bce9279..11fd44b 100644
--- a/ui/docs/calculator-ux.md
+++ b/ui/docs/calculator-ux.md
@@ -24,28 +24,60 @@ in as a per-ship result rather than a separate mode.
 
 1. **Ship Class design area** — five blocks (drive, armament, weapons,
    shields, cargo) and four tech levels (drive, weapons, shields,
-   cargo). Tech defaults to the player's current tech and shows a lock
-   icon once overridden; clicking it resets to the default.
+   cargo). Tech defaults to the player's current tech: the cell renders
+   the inherited number with an open padlock; clicking the open lock
+   activates an input (closed padlock), where the player may type an
+   override at or above their current tech. Clicking the closed
+   padlock resets to the default. The padlock slot is always reserved,
+   so the column width does not shift as the lock state toggles. The
+   inherited tech value reads through the same 3-decimal `Ceil3`
+   formatter the report uses, so the column lines up with derived
+   values. **Every numeric input in the calculator hides the native
+   spinner and drives stepping through ArrowUp / ArrowDown.** This keeps
+   the column widths stable, makes the inputs read consistently, and
+   gives each row a step that matches its purpose. The four ship-class
+   blocks (drive, weapons, shields, cargo) use a smart step that
+   respects the engine value rule (`0` or `≥ 1`): ArrowUp from 0 jumps
+   straight to 1, otherwise +0.1; ArrowDown from 1 collapses to 0,
+   otherwise −0.1, never producing an invalid value in `(0, 1)`.
+   Armament steps ±1 (clamped at 0). Tech, planet MAT, custom load,
+   lock value, and modernization target tech each step by their natural
+   grain (±0.001 for tech and lock values, ±0.01 for MAT and load).
 2. **Calculator area** — derived results: empty/loaded mass, empty/
    loaded speed, attack, defence, bombing (per ship), cargo capacity.
    A load toggle (empty / full / custom) sets the cargo load (in cargo
    units) that the loaded-column results use. At **full** the toggle
    shows the ship's cargo capacity; a **custom** load over that capacity
    is flagged as an error. With a zero cargo block there is no hold, so
-   the load is pinned to empty and the toggle is disabled.
+   the load is pinned to empty and the toggle is disabled. The bombing
+   and cargo-capacity rows have no goal-seek lock, but they still
+   reserve a hidden lock-slot placeholder so the value column stays
+   vertically aligned with the lockable rows above.
 3. **Planet area** — when an own planet is selected on the map, shows
    its MAT (overridable) and the single-turn build rate (ships per turn,
-   turns per ship). The realistic multi-turn forecast with CAP/COL
-   supply is planned (see ../ROADMAP.md).
+   turns per ship). The MAT follows the same lock idiom as the tech
+   cells: the planet number renders with an open padlock, clicking
+   opens an input with a closed padlock, and the closed padlock resets
+   to the planet value. The MAT label reads through the same 3-decimal
+   `Ceil3` formatter, matching the rest of the calculator's label
+   values. The realistic multi-turn forecast with CAP/COL supply is
+   planned (see ../ROADMAP.md).
 
 ## Locks and goal-seek
 
-Two distinct lock semantics share one icon (a closed padlock; it only
-appears once a value is pinned, click to release):
+Two distinct lock semantics share one padlock affordance. Both follow
+the same idiom — an open padlock (🔓) means *value is inherited /
+derived, click to override*; a closed padlock (🔒) means *value is
+pinned by the player, click to reset*:
 
 - **Override locks** on inputs that have a default — the four techs and
-  the planet MAT. Editing one overrides the default; the lock resets it.
-  Any number may be overridden at once.
+  the planet MAT. By default the cell shows the inherited number plus
+  an open padlock; clicking it switches to an input plus a closed
+  padlock for typing the override. Closing (clicking the closed
+  padlock) resets to the default. Any number may be overridden at once.
+  Tech overrides are floored at the player's current tech on this
+  turn — a lower value is flagged as invalid. The same floor applies
+  to the modernization target tech.
 - **Goal-seek locks** on derived results. Pinning a result back-solves
   the single input it claims, which then renders read-only (computed):
 
@@ -60,12 +92,19 @@ appears once a value is pinned, click to release):
 
   Only **one** result may be locked at a time (the others' lock
   affordances disable with a tooltip). An unreachable target — e.g. a
-  speed at or above the stripped-hull ceiling `20 × driveTech`, or a
-  solved block that fails the value rules — leaves the locked cell in a
-  red error state and does not apply. Inverse solving lives in
-  `pkg/calc/solve.go`; the bisection for defence → shields is the only
-  non-analytic case. Locking a speed is disabled when the drive block is
-  zero (a deliberately immobile ship has no speed to back-solve).
+  speed above the stripped-hull ceiling `20 × driveTech`, or a solved
+  block that fails the value rules (a DWSC value in the `(0, 1)` gap)
+  — leaves the locked cell in a red error state and does not apply.
+  When that happens the claimed block is **not** back-solved into the
+  invalid range; the design preview keeps reading the user's typed
+  values, so the row never silently shows a sub-1 block. Inverse
+  solving lives in `pkg/calc/solve.go`; the bisection for defence →
+  shields is the only non-analytic case. Locking a speed is disabled
+  when the drive block is zero (a deliberately immobile ship has no
+  speed to back-solve). With the drive block as the only non-zero mass
+  the displayed speed equals the ceiling exactly (every positive drive
+  gives the same speed), so the solver accepts that ceiling target as
+  a feasible lock and any positive drive solves it.
 
 ## Validation and display
 
@@ -75,25 +114,43 @@ negative, the five blocks follow the engine value rules
 (`pkg/calc/validator.go`, surfaced per-field by
 `shipClassFieldErrors`), and a custom load may not exceed cargo capacity.
 
-Every displayed number — the derived results and the goal-seek
-back-solved input — is rounded **up** to three decimals through the
-shared `pkg/calc/number.go.Ceil3` (bridged as `core.ceil3`), so a value
-is never shown lower than it is (a speed of 5.0003 reads 5.001). The
-engine keeps its own round-to-nearest `util.Fixed*`; `Ceil3` is a
-display-only helper that lives in `pkg/calc` so the UI and Go share one
-implementation.
+Every displayed number — the derived results, the inherited tech /
+planet MAT labels, and the goal-seek back-solved input — is rounded
+**up** to three decimals through the shared `pkg/calc/number.go.Ceil3`
+(bridged as `core.ceil3`) and always padded to three decimals so the
+column reads the same on integers and fractions alike (a speed of 20
+shows as `20.000`, of 5.0003 as `5.001`). Labels and inputs use the
+monospace stack from the design tokens (`--font-mono`) with
+right-aligned, tabular numerals so values line up vertically across
+rows. To match the display rule, every number input also refuses a
+fourth decimal as the user types: typing `1.2345` clamps the input to
+`1.234` on input. The engine keeps its own round-to-nearest
+`util.Fixed*`; `Ceil3` is a display-only helper that lives in `pkg/calc`
+so the UI and Go share one implementation.
 
-## Create / load / delete
+## Create / load
 
 The name field is a combobox over the player's existing classes. Picking
 an existing class loads it as a template (so you can tweak and Create a
 new one); Create is disabled while the name is invalid or duplicate
-(reusing `lib/util/ship-class-validation.ts`). When a saved class is
-loaded, a Delete affordance appears. Create / Delete reuse the existing
-`createShipClass` / `removeShipClass` order-draft flow, so the optimistic
-overlay reflects the change immediately. Ship classes are immutable after
-creation (per `game/rules.txt`), so there is no edit — only Create-new
-and Delete.
+(reusing `lib/util/ship-class-validation.ts`). Create reuses the existing
+`createShipClass` order-draft flow, so the optimistic overlay reflects
+the change immediately. Ship classes are immutable after creation (per
+`game/rules.txt`), so there is no edit — only Create-new. Delete-class
+lives in the ship-classes table (`lib/active-view/table-ship-classes.svelte`),
+not the calculator.
+
+Selecting a class from the dropdown loads it **immediately**, the
+moment the option is clicked. (Native `change` only fires on blur in
+Firefox; switching the load trigger to `input` makes the load
+synchronous everywhere, since the `InputEvent.inputType` flags a
+datalist replacement as `"insertReplacementText"` in Chromium / WebKit
+or `undefined` in Firefox — keyboard typing always carries a typing
+`inputType`.) If the live blocks differ from the previously loaded
+class (or, when nothing is loaded, from the empty defaults), the
+calculator first asks `Discard unsaved changes and load class «…»?`
+through a `window.confirm`; declining reverts the name field and
+leaves the current blocks untouched.
 
 ## Reach circles
 
diff --git a/ui/frontend/src/lib/calculator/calc-model.ts b/ui/frontend/src/lib/calculator/calc-model.ts
index bb4c586..45d76c1 100644
--- a/ui/frontend/src/lib/calculator/calc-model.ts
+++ b/ui/frontend/src/lib/calculator/calc-model.ts
@@ -92,6 +92,18 @@ export interface CalculatorResult {
 	outputs: CalculatorOutputs | null;
 }
 
+// isClaimedBlockValid checks that a solver result, before we apply it
+// to the resolved blocks, satisfies the same per-field rules the live
+// validator enforces on user-typed values (`pkg/calc/validator.go` /
+// `lib/util/ship-class-validation`). The four claimable blocks all
+// share the DWSC rule, so a single predicate suffices. Used to flag
+// a goal-seek target as infeasible when the only block that would
+// reach it falls in the (0, 1) gap.
+function isClaimedBlockValid(solved: number): boolean {
+	if (!Number.isFinite(solved)) return false;
+	return solved === 0 || solved >= 1;
+}
+
 function resolveLoad(
 	mode: LoadMode,
 	customLoad: number,
@@ -225,8 +237,18 @@ export function computeCalculator(
 			if (solved === null) {
 				lockFeasible = false;
 			} else {
-				blocks[claimed] = solved;
-				computedInput = claimed;
+				// The solver may produce a value that is mathematically
+				// correct yet rejected by the ship-class value rules —
+				// most commonly a DWSC block in the (0, 1) gap. Surface
+				// that as an infeasible lock so the lock input flips
+				// red and the outputs are suppressed, instead of
+				// silently showing an invalid design.
+				if (!isClaimedBlockValid(solved)) {
+					lockFeasible = false;
+				} else {
+					blocks[claimed] = solved;
+					computedInput = claimed;
+				}
 			}
 		}
 	}
diff --git a/ui/frontend/src/lib/calculator/ship-design-area.svelte b/ui/frontend/src/lib/calculator/ship-design-area.svelte
index fa2a7b4..48e9cac 100644
--- a/ui/frontend/src/lib/calculator/ship-design-area.svelte
+++ b/ui/frontend/src/lib/calculator/ship-design-area.svelte
@@ -1,13 +1,17 @@
 <!--
 Reusable "Ship Class design area": the five design blocks (drive,
 armament, weapons, shields, cargo) plus the four tech levels they are
-built with. Each tech defaults to the player's current level and shows a
-lock icon once overridden; clicking the lock resets it. A block claimed
-by an active goal-seek lock renders read-only with its own lock marker.
-The component is presentational — the parent owns the state and the
+built with. Tech and MAT locks follow the same idiom as goal-seek
+locks below the design area — by default the value renders as plain
+text with an open padlock; clicking it overrides (input + closed
+padlock). Reserved space for the padlock keeps the column width
+stable as the lock state toggles. A block claimed by an active
+goal-seek lock renders read-only with its own lock marker. The
+component is presentational — the parent owns the state and the
 calculator math — so the ship-group upgrade flow can reuse it later.
 -->
 <script lang="ts">
+	import { tick } from "svelte";
 	import { i18n, type TranslationKey } from "$lib/i18n/index.svelte";
 	import {
 		shipClassFieldErrors,
@@ -37,8 +41,17 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		resolved: DesignBlocksState;
 		techs: TechState;
 		techOverridden: Record<TechKey, boolean>;
+		// Lower bound for the tech inputs: the player's current tech on
+		// this turn. A design cannot be built with tech below the player's
+		// own level, so we surface that as a per-field validation error.
+		techFloor: TechState;
 		computedInput?: ClaimedInput | null;
 		blocksReadonly?: boolean;
+		// Formatter applied to the read-only tech value and to the
+		// resolved (goal-seek) ship-block value. Same `fmt` as the
+		// rest of the calculator, passed in so the design area stays
+		// presentational and the parent owns the rounding policy.
+		formatNumber: (value: number) => string;
 		onTechInput: (key: TechKey) => void;
 		onResetTech: (key: TechKey) => void;
 	};
@@ -47,8 +60,10 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		resolved,
 		techs = $bindable(),
 		techOverridden,
+		techFloor,
 		computedInput = null,
 		blocksReadonly = false,
+		formatNumber,
 		onTechInput,
 		onResetTech,
 	}: Props = $props();
@@ -73,21 +88,93 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		return reason === undefined ? "" : i18n.t(VALUE_REASON_KEY[reason]);
 	}
 	function techError(key: TechKey): string {
-		return techs[key] < 0 ? i18n.t("game.calculator.invalid.tech_value") : "";
+		const value = techs[key];
+		if (value < 0) return i18n.t("game.calculator.invalid.tech_value");
+		if (value < techFloor[key]) {
+			return i18n.t("game.calculator.invalid.tech_below_current");
+		}
+		return "";
+	}
+
+	// Smart step on the four ship-class blocks (drive, weapons, shields,
+	// cargo): values must be 0 or ≥ 1 per `pkg/calc/validator.go`, so the
+	// native 0.01 step would produce invalid intermediates like 0.01.
+	// Up: 0 jumps straight to 1; otherwise +0.1. Down: 1 collapses to 0;
+	// otherwise −0.1 down to 1, clamped at 0. Armament uses a plain
+	// integer step (±1, clamped at 0) so it follows the same
+	// JS-driven idiom and we can hide the native spinner uniformly.
+	function bumpBlock(value: number, dir: 1 | -1): number {
+		if (dir === 1) {
+			if (value < 1) return 1;
+			return Math.round((value + 0.1) * 10) / 10;
+		}
+		if (value <= 1) return 0;
+		return Math.round((value - 0.1) * 10) / 10;
+	}
+	function bumpArmament(value: number, dir: 1 | -1): number {
+		const next = Math.trunc(value) + dir;
+		return next < 0 ? 0 : next;
+	}
+	function onBlockKey(
+		event: KeyboardEvent,
+		key: keyof DesignBlocksState,
+		smart: boolean,
+	): void {
+		const dir = event.key === "ArrowUp" ? 1 : event.key === "ArrowDown" ? -1 : 0;
+		if (dir === 0) return;
+		event.preventDefault();
+		blocks[key] = smart
+			? bumpBlock(blocks[key], dir)
+			: bumpArmament(blocks[key], dir);
+	}
+	// Tech / modernization-target inputs all use the same ±0.001 step
+	// with a per-row floor; lifted into a helper so the parent can
+	// reuse it (modernization area in `calculator-tab`).
+	function bumpTech(event: KeyboardEvent, key: TechKey): void {
+		const dir = event.key === "ArrowUp" ? 1 : event.key === "ArrowDown" ? -1 : 0;
+		if (dir === 0) return;
+		event.preventDefault();
+		const current = techs[key];
+		const next = Math.round((current + dir * 0.001) * 1000) / 1000;
+		const floor = techFloor[key];
+		techs[key] = next < floor ? floor : next;
+	}
+	// Refuse a fourth decimal as typing happens: keeps the calculator
+	// from ever displaying a >3-decimal fraction the user could not
+	// have intended (the calculator math is `Ceil3`-rounded for display
+	// anyway). Pairs with `bind:value` — `apply` overwrites the bound
+	// state when Svelte's own bind handler has already read the
+	// over-precise number.
+	function capDecimals(event: Event, apply: (next: number) => void): void {
+		const el = event.currentTarget as HTMLInputElement;
+		const txt = el.value;
+		const dot = txt.indexOf(".");
+		if (dot < 0 || txt.length - dot - 1 <= 3) return;
+		el.value = txt.slice(0, dot + 4);
+		apply(el.valueAsNumber);
 	}
 
 	const BLOCK_ROWS: {
 		key: keyof DesignBlocksState;
 		label: () => string;
-		step: string;
 		tech: TechKey | null;
+		smartStep: boolean;
 	}[] = [
-		{ key: "drive", label: () => i18n.t("game.calculator.field.drive"), step: "0.01", tech: "drive" },
-		{ key: "armament", label: () => i18n.t("game.calculator.field.armament"), step: "1", tech: null },
-		{ key: "weapons", label: () => i18n.t("game.calculator.field.weapons"), step: "0.01", tech: "weapons" },
-		{ key: "shields", label: () => i18n.t("game.calculator.field.shields"), step: "0.01", tech: "shields" },
-		{ key: "cargo", label: () => i18n.t("game.calculator.field.cargo"), step: "0.01", tech: "cargo" },
+		{ key: "drive", label: () => i18n.t("game.calculator.field.drive"), tech: "drive", smartStep: true },
+		{ key: "armament", label: () => i18n.t("game.calculator.field.armament"), tech: null, smartStep: false },
+		{ key: "weapons", label: () => i18n.t("game.calculator.field.weapons"), tech: "weapons", smartStep: true },
+		{ key: "shields", label: () => i18n.t("game.calculator.field.shields"), tech: "shields", smartStep: true },
+		{ key: "cargo", label: () => i18n.t("game.calculator.field.cargo"), tech: "cargo", smartStep: true },
 	];
+
+	const techInputEls: Partial<Record<TechKey, HTMLInputElement>> = {};
+
+	async function activateTechOverride(key: TechKey): Promise<void> {
+		onTechInput(key);
+		await tick();
+		techInputEls[key]?.focus();
+		techInputEls[key]?.select();
+	}
 </script>
 
 <div class="design" data-testid="calculator-design-area">
@@ -102,46 +189,50 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 			<span class="label">{row.label()}</span>
 			{#if isComputed}
 				<input
-					class="ship"
+					class="ship no-spin"
 					type="number"
-					step={row.step}
+					step="any"
 					readonly
-					value={resolved[row.key]}
+					value={formatNumber(resolved[row.key])}
 					data-computed="true"
 					data-testid={`calculator-block-${row.key}`}
 					title={i18n.t("game.calculator.lock.reset")}
 				/>
 			{:else}
 				<input
-					class="ship"
+					class="ship no-spin"
 					type="number"
-					step={row.step}
+					step="any"
 					min="0"
 					bind:value={blocks[row.key]}
 					readonly={blocksReadonly}
 					aria-invalid={blockError(row.key) !== "" ? "true" : "false"}
 					title={blockError(row.key)}
 					data-testid={`calculator-block-${row.key}`}
+					onkeydown={(e) => onBlockKey(e, row.key, row.smartStep)}
+					oninput={(e) => capDecimals(e, (v) => (blocks[row.key] = v))}
 				/>
 			{/if}
 			{#if row.tech !== null}
 				{@const techKey = row.tech}
 				<span class="tech-cell">
-					<input
-						class="tech"
-						type="number"
-						step="0.001"
-						min="0"
-						bind:value={techs[techKey]}
-						oninput={() => onTechInput(techKey)}
-						aria-invalid={techError(techKey) !== "" ? "true" : "false"}
-						title={techError(techKey)}
-						data-testid={`calculator-tech-${techKey}`}
-					/>
 					{#if techOverridden[techKey]}
+						<input
+							bind:this={techInputEls[techKey]}
+							class="tech no-spin"
+							type="number"
+							step="any"
+							min={techFloor[techKey]}
+							bind:value={techs[techKey]}
+							aria-invalid={techError(techKey) !== "" ? "true" : "false"}
+							title={techError(techKey)}
+							data-testid={`calculator-tech-${techKey}`}
+							onkeydown={(e) => bumpTech(e, techKey)}
+							oninput={(e) => capDecimals(e, (v) => (techs[techKey] = v))}
+						/>
 						<button
 							type="button"
-							class="lock"
+							class="lock active"
 							title={i18n.t("game.calculator.tech.reset")}
 							aria-label={i18n.t("game.calculator.tech.reset")}
 							data-testid={`calculator-tech-reset-${techKey}`}
@@ -149,6 +240,23 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 						>
 							🔒
 						</button>
+					{:else}
+						<span
+							class="tech-val"
+							data-testid={`calculator-tech-value-${techKey}`}
+						>
+							{formatNumber(techs[techKey])}
+						</span>
+						<button
+							type="button"
+							class="lock"
+							title={i18n.t("game.calculator.tech.override")}
+							aria-label={i18n.t("game.calculator.tech.override")}
+							data-testid={`calculator-tech-override-${techKey}`}
+							onclick={() => void activateTechOverride(techKey)}
+						>
+							🔓
+						</button>
 					{/if}
 				</span>
 			{:else}
@@ -182,7 +290,7 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		font-size: 0.8rem;
 	}
 	input {
-		font: inherit;
+		font-family: var(--font-mono);
 		font-size: 0.8rem;
 		width: 100%;
 		min-width: 0;
@@ -192,6 +300,19 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		border: 1px solid var(--color-border);
 		border-radius: 3px;
 		font-variant-numeric: tabular-nums;
+		text-align: right;
+	}
+	/* Hide native spinners across the design area — the row drives
+	   every numeric edit through ArrowUp/ArrowDown so the column
+	   width stays stable and the inputs read consistently. */
+	input.no-spin::-webkit-inner-spin-button,
+	input.no-spin::-webkit-outer-spin-button {
+		-webkit-appearance: none;
+		margin: 0;
+	}
+	input.no-spin {
+		-moz-appearance: textfield;
+		appearance: textfield;
 	}
 	input[data-computed="true"],
 	input[readonly] {
@@ -206,6 +327,15 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		align-items: center;
 		gap: 0.2rem;
 	}
+	.tech-val {
+		flex: 1;
+		min-width: 0;
+		font-family: var(--font-mono);
+		font-size: 0.8rem;
+		font-variant-numeric: tabular-nums;
+		text-align: right;
+		padding: 0.2rem 0.35rem;
+	}
 	.lock {
 		flex: none;
 		padding: 0;
@@ -214,5 +344,10 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		background: transparent;
 		border: 0;
 		cursor: pointer;
+		opacity: 0.5;
+	}
+	.lock.active,
+	.lock:hover {
+		opacity: 1;
 	}
 </style>
diff --git a/ui/frontend/src/lib/i18n/locales/en.ts b/ui/frontend/src/lib/i18n/locales/en.ts
index 3fc975d..57031a0 100644
--- a/ui/frontend/src/lib/i18n/locales/en.ts
+++ b/ui/frontend/src/lib/i18n/locales/en.ts
@@ -364,7 +364,6 @@ const en = {
 	"game.calculator.name.placeholder": "new class name",
 	"game.calculator.name.existing": "your ship classes",
 	"game.calculator.action.create": "create",
-	"game.calculator.action.delete": "delete",
 	"game.calculator.col.ship": "ship",
 	"game.calculator.col.tech": "tech",
 	"game.calculator.field.drive": "drive",
@@ -393,7 +392,9 @@ const en = {
 	"game.calculator.lock.reset": "locked — click to release to the computed value",
 	"game.calculator.lock.infeasible": "this target cannot be reached with the current design",
 	"game.calculator.lock.max": "release the locked result first — one result at a time",
+	"game.calculator.tech.override": "click to override your current tech",
 	"game.calculator.tech.reset": "overridden — click to reset to your current tech",
+	"game.calculator.mat.override": "click to override the planet value",
 	"game.calculator.mat.reset": "overridden — click to reset to the planet value",
 	"game.calculator.modern.current": "current",
 	"game.calculator.modern.target": "target",
@@ -418,8 +419,10 @@ const en = {
 	"game.calculator.invalid.all_zero": "at least one value must be nonzero",
 	"game.calculator.invalid.negative": "value cannot be negative",
 	"game.calculator.invalid.tech_value": "tech level cannot be negative",
+	"game.calculator.invalid.tech_below_current": "tech level cannot be below your current tech this turn",
 	"game.calculator.invalid.load_over_capacity": "load exceeds the ship's cargo capacity",
 	"game.calculator.lock.no_drive": "set a non-zero drive before locking speed",
+	"game.calculator.confirm_reset_for_load": "Discard unsaved changes and load class «{name}»?",
 
 	"game.table.sciences.title": "sciences",
 	"game.table.sciences.column.name": "name",
diff --git a/ui/frontend/src/lib/i18n/locales/ru.ts b/ui/frontend/src/lib/i18n/locales/ru.ts
index dc33c27..b6ac94b 100644
--- a/ui/frontend/src/lib/i18n/locales/ru.ts
+++ b/ui/frontend/src/lib/i18n/locales/ru.ts
@@ -365,7 +365,6 @@ const ru: Record<keyof typeof en, string> = {
 	"game.calculator.name.placeholder": "имя нового класса",
 	"game.calculator.name.existing": "ваши классы кораблей",
 	"game.calculator.action.create": "создать",
-	"game.calculator.action.delete": "удалить",
 	"game.calculator.col.ship": "корабль",
 	"game.calculator.col.tech": "технологии",
 	"game.calculator.field.drive": "двигатель",
@@ -394,7 +393,9 @@ const ru: Record<keyof typeof en, string> = {
 	"game.calculator.lock.reset": "зафиксировано — нажмите, чтобы вернуть вычисляемое значение",
 	"game.calculator.lock.infeasible": "эта цель недостижима при текущих параметрах",
 	"game.calculator.lock.max": "сначала снимите фиксацию с другого результата — по одному за раз",
+	"game.calculator.tech.override": "нажмите, чтобы задать свой технологический уровень",
 	"game.calculator.tech.reset": "переопределено — нажмите, чтобы вернуть ваши текущие технологии",
+	"game.calculator.mat.override": "нажмите, чтобы задать своё значение MAT",
 	"game.calculator.mat.reset": "переопределено — нажмите, чтобы вернуть значение планеты",
 	"game.calculator.modern.current": "текущий",
 	"game.calculator.modern.target": "целевой",
@@ -419,8 +420,10 @@ const ru: Record<keyof typeof en, string> = {
 	"game.calculator.invalid.all_zero": "хотя бы одно значение должно быть ненулевым",
 	"game.calculator.invalid.negative": "значение не может быть отрицательным",
 	"game.calculator.invalid.tech_value": "технологический уровень не может быть отрицательным",
+	"game.calculator.invalid.tech_below_current": "технологический уровень не может быть ниже ваших текущих технологий на этом ходу",
 	"game.calculator.invalid.load_over_capacity": "загрузка превышает грузоподъёмность корабля",
 	"game.calculator.lock.no_drive": "задайте ненулевой двигатель, прежде чем фиксировать скорость",
+	"game.calculator.confirm_reset_for_load": "Сбросить несохранённые изменения и загрузить класс «{name}»?",
 
 	"game.table.sciences.title": "науки",
 	"game.table.sciences.column.name": "название",
diff --git a/ui/frontend/src/lib/sidebar/calculator-tab.svelte b/ui/frontend/src/lib/sidebar/calculator-tab.svelte
index d306441..5cb7dc0 100644
--- a/ui/frontend/src/lib/sidebar/calculator-tab.svelte
+++ b/ui/frontend/src/lib/sidebar/calculator-tab.svelte
@@ -14,7 +14,7 @@ switch (the inspector auto-opens on a planet click) — the calculator is a
 long-lived planning tool. `ensureGame` resets it when the game changes.
 -->
 <script lang="ts">
-	import { getContext } from "svelte";
+	import { getContext, tick } from "svelte";
 	import { appScreen } from "$lib/app-nav.svelte";
 
 	import { i18n, type TranslationKey } from "$lib/i18n/index.svelte";
@@ -204,11 +204,6 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		nameValidation.ok ? "" : i18n.t(nameInvalidKeyMap[nameValidation.reason]),
 	);
 	const canCreate = $derived(nameValidation.ok && draft !== undefined);
-	const canDelete = $derived(
-		cs.loadedExisting !== null &&
-			existingNames.includes(cs.loadedExisting) &&
-			draft !== undefined,
-	);
 
 	// Per-block modernization upgrade cost (current tech → target tech).
 	const modernCosts = $derived.by(() => {
@@ -237,12 +232,35 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 
 	// Display every computed number rounded up to three decimals via the
 	// shared `Ceil3` bridge, so a value is never shown lower than it is.
+	// Always three decimals (`1` → `1.000`) for column-aligned readability,
+	// and without thousands grouping so the same string also embeds in the
+	// read-only goal-seek `<input type="number">` cell.
 	function fmt(value: number | null | undefined): string {
 		if (value === null || value === undefined) {
 			return i18n.t("game.calculator.unavailable");
 		}
 		const rounded = core !== null ? core.ceil3({ value }) : value;
-		return rounded.toLocaleString(undefined, { maximumFractionDigits: 3 });
+		return rounded.toLocaleString(undefined, {
+			minimumFractionDigits: 3,
+			maximumFractionDigits: 3,
+			useGrouping: false,
+		});
+	}
+
+	// Cap typed precision at three decimal digits. Number inputs use
+	// `step="any"`, which lets the browser accept arbitrary precision; the
+	// owner asked us to refuse a fourth decimal as typing happens so the
+	// calculator never displays a longer-than-three-digit fraction. Pairs
+	// with `bind:value`: if Svelte's bind handler has already read the
+	// over-precise number, `apply` overwrites the state with the truncated
+	// value so the next reactive flush does not undo our truncation.
+	function capDecimals(event: Event, apply: (next: number) => void): void {
+		const el = event.currentTarget as HTMLInputElement;
+		const txt = el.value;
+		const dot = txt.indexOf(".");
+		if (dot < 0 || txt.length - dot - 1 <= 3) return;
+		el.value = txt.slice(0, dot + 4);
+		apply(el.valueAsNumber);
 	}
 
 	// The goal-seek back-solved block, shown in its read-only cell, is
@@ -273,6 +291,18 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cs.matValue < 0 ? i18n.t("game.calculator.invalid.negative") : "",
 	);
 
+	// Modernization target tech mirrors the design-area floor: a target
+	// below the player's current tech on this turn is meaningless (no
+	// upgrade), so flag it the same way.
+	function targetTechError(key: TechKey): string {
+		const value = cs.targetTech[key];
+		if (value < 0) return i18n.t("game.calculator.invalid.negative");
+		if (value < playerTech[key]) {
+			return i18n.t("game.calculator.invalid.tech_below_current");
+		}
+		return "";
+	}
+
 	// Locking a speed back-solves the drive block; with a zero drive the
 	// ship is deliberately immobile, so disallow it.
 	function lockDisabledReason(output: LockableOutputId): string {
@@ -291,8 +321,12 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	function onResetTech(key: TechKey): void {
 		cs.techOverridden[key] = false;
 	}
-	function onMatInput(): void {
+	const matInputRef: { el?: HTMLInputElement } = {};
+	async function activateMatOverride(): Promise<void> {
 		cs.matOverridden = true;
+		await tick();
+		matInputRef.el?.focus();
+		matInputRef.el?.select();
 	}
 	function resetMat(): void {
 		cs.matOverridden = false;
@@ -307,6 +341,30 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cs.lock = null;
 	}
 
+	// Generic ±step keyboard handler for the calculator's free-form
+	// number inputs (MAT, custom-load, lock value, modernization
+	// target tech). Pairs with `class="no-spin"` so the native spinner
+	// is hidden everywhere and the column width is stable; ArrowUp /
+	// ArrowDown is the only step affordance. The smart 0↔1 jump on
+	// the ship-class blocks lives in `ship-design-area.svelte` —
+	// these other inputs accept any non-negative number.
+	function onStepKey(
+		event: KeyboardEvent,
+		current: number,
+		step: number,
+		min: number,
+		apply: (next: number) => void,
+	): void {
+		const dir = event.key === "ArrowUp" ? 1 : event.key === "ArrowDown" ? -1 : 0;
+		if (dir === 0) return;
+		event.preventDefault();
+		// Snap to the same fractional grid as `step` so 0.001 stays
+		// at three decimals instead of drifting via float math.
+		const inv = 1 / step;
+		const next = Math.round((current + dir * step) * inv) / inv;
+		apply(next < min ? min : next);
+	}
+
 	function loadExisting(clsName: string): void {
 		const cls = localShipClass.find((c) => c.name === clsName);
 		if (cls === undefined) return;
@@ -322,6 +380,78 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cs.lock = null;
 	}
 
+	// Compare the live blocks to the baseline they were last loaded
+	// from — or to the empty defaults if no class has been loaded. The
+	// dropdown selection flow uses this to ask before discarding manual
+	// edits. Tech overrides are independent of class loading, so they
+	// don't count as "dirty" here.
+	function baselineBlocks(): {
+		drive: number;
+		armament: number;
+		weapons: number;
+		shields: number;
+		cargo: number;
+	} {
+		if (cs.loadedExisting !== null) {
+			const cls = localShipClass.find((c) => c.name === cs.loadedExisting);
+			if (cls !== undefined) {
+				return {
+					drive: cls.drive,
+					armament: cls.armament,
+					weapons: cls.weapons,
+					shields: cls.shields,
+					cargo: cls.cargo,
+				};
+			}
+		}
+		return { drive: 0, armament: 0, weapons: 0, shields: 0, cargo: 0 };
+	}
+	function isDesignDirty(): boolean {
+		const base = baselineBlocks();
+		return (
+			cs.blocks.drive !== base.drive ||
+			cs.blocks.armament !== base.armament ||
+			cs.blocks.weapons !== base.weapons ||
+			cs.blocks.shields !== base.shields ||
+			cs.blocks.cargo !== base.cargo
+		);
+	}
+	function tryLoadByName(name: string): void {
+		const cls = localShipClass.find((c) => c.name === name);
+		if (cls === undefined) return;
+		if (cs.loadedExisting === cls.name) return;
+		if (isDesignDirty()) {
+			const ok = window.confirm(
+				i18n.t("game.calculator.confirm_reset_for_load", {
+					name: cls.name,
+				}),
+			);
+			if (!ok) {
+				cs.name = cs.loadedExisting ?? "";
+				return;
+			}
+		}
+		loadExisting(name);
+	}
+	// Catch the datalist option click immediately. Native `change` only
+	// fires on blur in Firefox, which is what made dropdown selection
+	// look delayed; `input` fires the moment the value is set. Typed
+	// keystrokes carry an `inputType` ("insertText", "deleteContent…");
+	// a datalist selection replaces the value in one shot, so its
+	// `inputType` is undefined (Firefox) or "insertReplacementText"
+	// (Chromium / WebKit). We treat that as a selection.
+	function onNameInput(event: Event): void {
+		const ev = event as InputEvent;
+		const isSelection =
+			ev.inputType === undefined ||
+			ev.inputType === "insertReplacementText";
+		if (!isSelection) {
+			cs.loadedExisting = null;
+			return;
+		}
+		tryLoadByName(cs.name);
+	}
+
 	// React to the ship-classes table / bottom-tabs asking to load a
 	// class (or start a fresh design) into the calculator. The layout
 	// flips the sidebar to this tab in parallel.
@@ -354,16 +484,6 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cs.loadedExisting = created.name;
 	}
 
-	async function deleteClass(): Promise<void> {
-		if (cs.loadedExisting === null || draft === undefined) return;
-		await draft.add({
-			kind: "removeShipClass",
-			id: crypto.randomUUID(),
-			name: cs.loadedExisting,
-		});
-		cs.loadedExisting = null;
-	}
-
 	const LOCK_LABELS: Record<LockableOutputId, string> = $derived({
 		emptyMass: i18n.t("game.calculator.out.mass"),
 		loadedMass: i18n.t("game.calculator.out.mass"),
@@ -378,9 +498,13 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	{#if cs.lock === output}
 		<span class="cell locked" class:infeasible={!result.lockFeasible}>
 			<input
+				class="no-spin"
 				type="number"
-				step="0.001"
+				step="any"
 				bind:value={cs.lockValue}
+				onkeydown={(e) =>
+					onStepKey(e, cs.lockValue, 0.001, 0, (v) => (cs.lockValue = v))}
+				oninput={(e) => capDecimals(e, (v) => (cs.lockValue = v))}
 				data-testid={`calculator-locked-${output}`}
 				title={result.lockFeasible ? "" : i18n.t("game.calculator.lock.infeasible")}
 			/>
@@ -446,8 +570,8 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 			placeholder={i18n.t("game.calculator.name.placeholder")}
 			maxlength="30"
 			bind:value={cs.name}
-			oninput={() => (cs.loadedExisting = null)}
-			onchange={() => loadExisting(cs.name)}
+			oninput={onNameInput}
+			onchange={() => tryLoadByName(cs.name)}
 			aria-invalid={nameValidation.ok ? "false" : "true"}
 			data-testid="calculator-name"
 		/>
@@ -469,23 +593,15 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 			</button>
 		{/if}
 	</div>
-	{#if cs.mode === "ship" && canDelete}
-		<button
-			type="button"
-			class="delete"
-			data-testid="calculator-delete"
-			onclick={() => void deleteClass()}
-		>
-			{i18n.t("game.calculator.action.delete")} {cs.loadedExisting}
-		</button>
-	{/if}
 
 	<ShipDesignArea
 		bind:blocks={cs.blocks}
 		resolved={resolvedCeil}
 		bind:techs={cs.techValues}
 		techOverridden={cs.techOverridden}
+		techFloor={playerTech}
 		computedInput={result.computedInput}
+		formatNumber={fmt}
 		{onTechInput}
 		{onResetTech}
 	/>
@@ -509,10 +625,13 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 			{#if cs.loadMode === "custom"}
 				<input
 					type="number"
-					step="0.01"
+					step="any"
 					min="0"
-					class="custom-load"
+					class="custom-load no-spin"
 					bind:value={cs.customLoad}
+					onkeydown={(e) =>
+						onStepKey(e, cs.customLoad, 0.01, 0, (v) => (cs.customLoad = v))}
+					oninput={(e) => capDecimals(e, (v) => (cs.customLoad = v))}
 					aria-invalid={customLoadError !== "" ? "true" : "false"}
 					title={customLoadError}
 					data-testid="calculator-custom-load"
@@ -560,6 +679,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 					<span class="val" data-testid="calculator-out-bombing">
 						{fmt(result.outputs?.bombing)}
 					</span>
+					<span class="lock-slot" aria-hidden="true">🔓</span>
 				</span>
 				<span></span>
 			</div>
@@ -569,6 +689,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 					<span class="val" data-testid="calculator-out-cargo-capacity">
 						{fmt(result.outputs === null ? null : result.cargoCapacity)}
 					</span>
+					<span class="lock-slot" aria-hidden="true">🔓</span>
 				</span>
 				<span></span>
 			</div>
@@ -589,17 +710,21 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 				<div class="rrow">
 					<span class="label">{i18n.t("game.calculator.planet.mat")}</span>
 					<span class="cell">
-						<input
-							type="number"
-							step="0.01"
-							min="0"
-							bind:value={cs.matValue}
-							oninput={onMatInput}
-							aria-invalid={matError !== "" ? "true" : "false"}
-							title={matError}
-							data-testid="calculator-planet-mat"
-						/>
 						{#if cs.matOverridden}
+							<input
+								bind:this={matInputRef.el}
+								class="no-spin"
+								type="number"
+								step="any"
+								min="0"
+								bind:value={cs.matValue}
+								onkeydown={(e) =>
+									onStepKey(e, cs.matValue, 0.01, 0, (v) => (cs.matValue = v))}
+								oninput={(e) => capDecimals(e, (v) => (cs.matValue = v))}
+								aria-invalid={matError !== "" ? "true" : "false"}
+								title={matError}
+								data-testid="calculator-planet-mat"
+							/>
 							<button
 								type="button"
 								class="lock active"
@@ -610,6 +735,23 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 							>
 								🔒
 							</button>
+						{:else}
+							<span
+								class="mat-val"
+								data-testid="calculator-planet-mat-value"
+							>
+								{fmt(cs.matValue)}
+							</span>
+							<button
+								type="button"
+								class="lock"
+								title={i18n.t("game.calculator.mat.override")}
+								aria-label={i18n.t("game.calculator.mat.override")}
+								data-testid="calculator-mat-override"
+								onclick={() => void activateMatOverride()}
+							>
+								🔓
+							</button>
 						{/if}
 					</span>
 					<span></span>
@@ -638,18 +780,28 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 				<span class="col-head">{i18n.t("game.calculator.modern.cost")}</span>
 			</div>
 			{#each modernCosts?.perBlock ?? [] as row (row.key)}
+				{@const targetError = targetTechError(row.key)}
 				<div class="rrow">
 					<span class="label">{i18n.t(`game.calculator.field.${row.key}` as TranslationKey)}</span>
 					<span class="cell">
 						<input
+							class="no-spin"
 							type="number"
-							step="0.001"
-							min="0"
+							step="any"
+							min={playerTech[row.key]}
 							bind:value={cs.targetTech[row.key]}
-							aria-invalid={cs.targetTech[row.key] < 0 ? "true" : "false"}
-							title={cs.targetTech[row.key] < 0
-								? i18n.t("game.calculator.invalid.negative")
-								: ""}
+							onkeydown={(e) =>
+								onStepKey(
+									e,
+									cs.targetTech[row.key],
+									0.001,
+									playerTech[row.key],
+									(v) => (cs.targetTech[row.key] = v),
+								)}
+							oninput={(e) =>
+								capDecimals(e, (v) => (cs.targetTech[row.key] = v))}
+							aria-invalid={targetError !== "" ? "true" : "false"}
+							title={targetError}
 							data-testid={`calculator-target-${row.key}`}
 						/>
 					</span>
@@ -718,8 +870,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	.name[aria-invalid="true"] {
 		border-color: var(--color-danger);
 	}
-	.create,
-	.delete {
+	.create {
 		font: inherit;
 		font-size: 0.8rem;
 		padding: 0.25rem 0.55rem;
@@ -737,10 +888,6 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		opacity: 0.5;
 		cursor: not-allowed;
 	}
-	.delete {
-		color: var(--color-danger);
-		align-self: flex-start;
-	}
 	.load {
 		display: flex;
 		align-items: center;
@@ -766,13 +913,15 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	}
 	.custom-load {
 		width: 4rem;
-		font: inherit;
+		font-family: var(--font-mono);
 		font-size: 0.8rem;
+		font-variant-numeric: tabular-nums;
 		padding: 0.15rem 0.3rem;
 		background: var(--color-bg);
 		color: var(--color-text);
 		border: 1px solid var(--color-border);
 		border-radius: 3px;
+		text-align: right;
 	}
 	.results,
 	.modern {
@@ -802,6 +951,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		justify-content: flex-end;
 	}
 	.cell .val {
+		font-family: var(--font-mono);
 		font-variant-numeric: tabular-nums;
 		font-size: 0.85rem;
 		text-align: right;
@@ -809,7 +959,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	.cell input {
 		width: 100%;
 		min-width: 0;
-		font: inherit;
+		font-family: var(--font-mono);
 		font-size: 0.8rem;
 		padding: 0.15rem 0.3rem;
 		background: var(--color-bg);
@@ -819,6 +969,19 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		font-variant-numeric: tabular-nums;
 		text-align: right;
 	}
+	/* Hide the native spinner on every calculator number input — the
+	   row drives every numeric edit through ArrowUp / ArrowDown so the
+	   column width is stable and the inputs read consistently with the
+	   ship-block row inside the design area. */
+	input.no-spin::-webkit-inner-spin-button,
+	input.no-spin::-webkit-outer-spin-button {
+		-webkit-appearance: none;
+		margin: 0;
+	}
+	input.no-spin {
+		-moz-appearance: textfield;
+		appearance: textfield;
+	}
 	.cell.locked input {
 		color: var(--color-accent);
 		border-color: var(--color-accent);
@@ -845,6 +1008,12 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cursor: not-allowed;
 		opacity: 0.2;
 	}
+	.lock-slot {
+		flex: none;
+		font-size: 0.7rem;
+		line-height: 1;
+		visibility: hidden;
+	}
 	.planet {
 		border-top: 1px solid var(--color-border-subtle);
 		padding-top: 0.5rem;
@@ -878,6 +1047,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	}
 	.planet-stats dd {
 		margin: 0;
+		font-family: var(--font-mono);
 		font-variant-numeric: tabular-nums;
 		font-size: 0.85rem;
 		text-align: right;
@@ -895,8 +1065,21 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cursor: not-allowed;
 	}
 	.full-capacity {
+		font-family: var(--font-mono);
 		font-variant-numeric: tabular-nums;
 		font-size: 0.8rem;
 		color: var(--color-accent);
 	}
+	/* Plain-text view of the planet MAT (mirrors `.tech-val` in the
+	   design area) so the cell width stays the same whether the value is
+	   the inherited planet number or the player's override. */
+	.mat-val {
+		flex: 1;
+		min-width: 0;
+		font-family: var(--font-mono);
+		font-size: 0.85rem;
+		font-variant-numeric: tabular-nums;
+		text-align: right;
+		padding: 0.15rem 0.3rem;
+	}
 </style>
diff --git a/ui/frontend/tests/calc-model.test.ts b/ui/frontend/tests/calc-model.test.ts
index 92e877d..84e1832 100644
--- a/ui/frontend/tests/calc-model.test.ts
+++ b/ui/frontend/tests/calc-model.test.ts
@@ -135,6 +135,56 @@ describe("computeCalculator goal-seek", () => {
 		expect(result.blocks.drive).toBe(10);
 	});
 
+	test("an attack target that back-solves to a (0, 1) weapons block is infeasible", () => {
+		// weapons = targetAttack / weaponsTech; weaponsTech=1.5, a 0.5
+		// target → weapons = 0.333…, which fails the DWSC rule (must be
+		// 0 or ≥ 1). The lock is flagged infeasible so the UI shows the
+		// red border, and the claimed block is left at its raw value so
+		// the design preview keeps reading off the user's own design.
+		const core = makeFakeCore();
+		const result = computeCalculator(
+			input({ lock: { output: "attack", value: 0.5 } }),
+			core,
+		);
+		expect(result.lockFeasible).toBe(false);
+		expect(result.computedInput).toBeNull();
+		// The claimed block stays at its raw value.
+		expect(result.blocks.weapons).toBe(0);
+	});
+
+	test("an empty-mass target that back-solves to a (0, 1) cargo block is infeasible", () => {
+		// emptyMass = drive + shields + cargo; with drive=10 shields=5,
+		// rest excluding cargo = 15. Target 15.5 → cargo = 0.5, in the
+		// invalid gap, so the lock is flagged.
+		const core = makeFakeCore();
+		const result = computeCalculator(
+			input({ lock: { output: "emptyMass", value: 15.5 } }),
+			core,
+		);
+		expect(result.lockFeasible).toBe(false);
+		expect(result.computedInput).toBeNull();
+		expect(result.blocks.cargo).toBe(5);
+	});
+
+	test("speed lock is feasible at the ceiling when rest mass is zero", () => {
+		// Regression for the D=1, W=A=S=C=0 case: every block except
+		// drive is zero, so speed equals 20*driveTech (the ceiling); the
+		// solver must accept that exact target instead of flagging it
+		// as unreachable.
+		const core = makeFakeCore();
+		const result = computeCalculator(
+			input({
+				blocks: { drive: 1, armament: 0, weapons: 0, shields: 0, cargo: 0 },
+				driveTech: 1,
+				lock: { output: "speedEmpty", value: 20 },
+			}),
+			core,
+		);
+		expect(result.lockFeasible).toBe(true);
+		expect(result.computedInput).toBe("drive");
+		expect(result.outputs?.speedEmpty).toBeCloseTo(20, 9);
+	});
+
 	test("calls the matching solver with the right context", () => {
 		const weaponsForAttack = vi.fn(() => 7);
 		const core = makeFakeCore({ weaponsForAttack });
diff --git a/ui/frontend/tests/calculator-tab.test.ts b/ui/frontend/tests/calculator-tab.test.ts
index 96a1ca4..52c942d 100644
--- a/ui/frontend/tests/calculator-tab.test.ts
+++ b/ui/frontend/tests/calculator-tab.test.ts
@@ -278,4 +278,390 @@ describe("calculator-tab", () => {
 			"15.273",
 		);
 	});
+
+	test("tech defaults render as a number with an open-lock affordance", () => {
+		const ui = mount();
+		// Default state: no override → number + open lock, no input.
+		expect(ui.getByTestId("calculator-tech-value-drive")).toHaveTextContent(
+			"1.2",
+		);
+		expect(
+			ui.getByTestId("calculator-tech-override-drive"),
+		).toBeInTheDocument();
+		expect(ui.queryByTestId("calculator-tech-drive")).toBeNull();
+	});
+
+	test("clicking the open tech lock reveals the input + closed lock", async () => {
+		const ui = mount();
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		// Now an input is rendered and the lock turned closed (reset).
+		expect(ui.getByTestId("calculator-tech-drive")).toHaveValue(1.2);
+		expect(ui.getByTestId("calculator-tech-reset-drive")).toBeInTheDocument();
+		expect(ui.queryByTestId("calculator-tech-value-drive")).toBeNull();
+	});
+
+	test("flags a tech override below the player's current tech", async () => {
+		const ui = mount();
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		// Player drive is 1.2; setting 0.5 is below the floor.
+		await fireEvent.input(ui.getByTestId("calculator-tech-drive"), {
+			target: { value: "0.5" },
+		});
+		expect(ui.getByTestId("calculator-tech-drive")).toHaveAttribute(
+			"aria-invalid",
+			"true",
+		);
+	});
+
+	test("smart step jumps from 0 to 1 on ArrowUp for ship blocks", async () => {
+		const ui = mount();
+		const drive = ui.getByTestId("calculator-block-drive") as HTMLInputElement;
+		drive.focus();
+		await fireEvent.keyDown(drive, { key: "ArrowUp" });
+		expect(drive).toHaveValue(1);
+		await fireEvent.keyDown(drive, { key: "ArrowUp" });
+		expect(drive).toHaveValue(1.1);
+		await fireEvent.keyDown(drive, { key: "ArrowDown" });
+		expect(drive).toHaveValue(1);
+		await fireEvent.keyDown(drive, { key: "ArrowDown" });
+		expect(drive).toHaveValue(0);
+	});
+
+	test("regression: speed lock works at the ceiling with all-zero non-drive blocks", async () => {
+		const ui = mount();
+		await setBlock(ui, "drive", 1);
+		// Override drive tech to 1 so the ceiling math is plain.
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		await fireEvent.input(ui.getByTestId("calculator-tech-drive"), {
+			target: { value: "1" },
+		});
+		// With D=1, W=A=S=C=0 the only achievable speed is 20*driveTech=20.
+		expect(ui.getByTestId("calculator-out-speedEmpty")).toHaveTextContent("20");
+		await fireEvent.click(ui.getByTestId("calculator-lock-speedEmpty"));
+		const locked = ui.getByTestId("calculator-locked-speedEmpty");
+		expect(locked).toHaveValue(20);
+		// The lock is feasible — no infeasible title and no red error class.
+		expect(locked).not.toHaveAttribute(
+			"title",
+			expect.stringMatching(/cannot be reached/i),
+		);
+	});
+
+	test("planet MAT defaults to a value + open lock and opens an input on click", async () => {
+		const selection = new SelectionStore();
+		selection.selectPlanet(17);
+		const ui = mount({
+			report: makeReport({ planets: [LOCAL_PLANET] }),
+			selection,
+		});
+		// Initial state: the MAT shows the planet's value via the number cell
+		// and an open lock; no input until the override is activated.
+		expect(
+			ui.getByTestId("calculator-planet-mat-value"),
+		).toHaveTextContent("100");
+		expect(
+			ui.getByTestId("calculator-mat-override"),
+		).toBeInTheDocument();
+		expect(ui.queryByTestId("calculator-planet-mat")).toBeNull();
+		await fireEvent.click(ui.getByTestId("calculator-mat-override"));
+		expect(ui.getByTestId("calculator-planet-mat")).toHaveValue(100);
+		expect(ui.getByTestId("calculator-mat-reset")).toBeInTheDocument();
+	});
+
+	test("flags a modernization target below the player's current tech", async () => {
+		const ui = mount();
+		await fireEvent.click(ui.getByTestId("calculator-mode-modernization"));
+		// Player drive is 1.2; the target is seeded with the same value.
+		await fireEvent.input(ui.getByTestId("calculator-target-drive"), {
+			target: { value: "0.5" },
+		});
+		expect(ui.getByTestId("calculator-target-drive")).toHaveAttribute(
+			"aria-invalid",
+			"true",
+		);
+	});
+
+	test("armament Arrow keys step the integer block by ±1 (clamped at 0)", async () => {
+		const ui = mount();
+		const armament = ui.getByTestId(
+			"calculator-block-armament",
+		) as HTMLInputElement;
+		armament.focus();
+		await fireEvent.keyDown(armament, { key: "ArrowUp" });
+		expect(armament).toHaveValue(1);
+		await fireEvent.keyDown(armament, { key: "ArrowUp" });
+		expect(armament).toHaveValue(2);
+		await fireEvent.keyDown(armament, { key: "ArrowDown" });
+		expect(armament).toHaveValue(1);
+		await fireEvent.keyDown(armament, { key: "ArrowDown" });
+		expect(armament).toHaveValue(0);
+		// Clamped at zero — another ArrowDown is a no-op.
+		await fireEvent.keyDown(armament, { key: "ArrowDown" });
+		expect(armament).toHaveValue(0);
+	});
+
+	test("renders unoverridden tech as a 3-decimal label (matches the report)", () => {
+		// Player drive tech 1.2 → "1.200" via the shared ceil3 formatter,
+		// always padded to three decimals (calculator labels are column-
+		// aligned with the report).
+		const ui = mount();
+		const tech = ui.getByTestId("calculator-tech-value-drive");
+		expect((tech.textContent ?? "").trim()).toBe("1.200");
+	});
+
+	test("planet MAT label renders through the 3-decimal formatter", () => {
+		const selection = new SelectionStore();
+		selection.selectPlanet(17);
+		const ui = mount({
+			report: makeReport({ planets: [LOCAL_PLANET] }),
+			selection,
+		});
+		// Planet MAT is 100 → "100.000" through the shared formatter; the
+		// label is monospaced + right-aligned via the existing `.mat-val`
+		// rule. Integer MAT pads to three decimals like every other label.
+		const mat = ui.getByTestId("calculator-planet-mat-value");
+		expect((mat.textContent ?? "").trim()).toBe("100.000");
+	});
+
+	test("derived results pad to three decimals (integer empty mass)", async () => {
+		// Integer-valued outputs read with the same trailing zeros as
+		// fractional ones — column-aligned tabular display.
+		const ui = mount();
+		await setBlock(ui, "drive", 10);
+		await setBlock(ui, "shields", 5);
+		await setBlock(ui, "cargo", 5);
+		const mass = ui.getByTestId("calculator-out-emptyMass");
+		expect((mass.textContent ?? "").trim()).toBe("20.000");
+	});
+
+	test("number inputs refuse a fourth decimal as the user types", async () => {
+		const selection = new SelectionStore();
+		selection.selectPlanet(17);
+		const ui = mount({
+			report: makeReport({ planets: [LOCAL_PLANET] }),
+			selection,
+		});
+		// MAT input: typed "12.3456" must clamp to "12.345" on input.
+		await fireEvent.click(ui.getByTestId("calculator-mat-override"));
+		const mat = ui.getByTestId("calculator-planet-mat") as HTMLInputElement;
+		await fireEvent.input(mat, { target: { value: "12.3456" } });
+		expect(mat.value).toBe("12.345");
+		expect(mat.valueAsNumber).toBeCloseTo(12.345, 9);
+
+		// Custom-load input on a ship with a non-zero cargo: typed
+		// "1.2345" must clamp to "1.234".
+		await setBlock(ui, "drive", 10);
+		await setBlock(ui, "shields", 5);
+		await setBlock(ui, "cargo", 5);
+		await fireEvent.click(ui.getByTestId("calculator-load-custom"));
+		const load = ui.getByTestId("calculator-custom-load") as HTMLInputElement;
+		await fireEvent.input(load, { target: { value: "1.2345" } });
+		expect(load.value).toBe("1.234");
+	});
+
+	test("tech and target-tech inputs cap at three decimals", async () => {
+		const ui = mount();
+		// Tech override input.
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		const tech = ui.getByTestId("calculator-tech-drive") as HTMLInputElement;
+		await fireEvent.input(tech, { target: { value: "2.9999" } });
+		expect(tech.value).toBe("2.999");
+
+		// Modernization target tech input.
+		await fireEvent.click(ui.getByTestId("calculator-mode-modernization"));
+		const target = ui.getByTestId(
+			"calculator-target-drive",
+		) as HTMLInputElement;
+		await fireEvent.input(target, { target: { value: "3.1416" } });
+		expect(target.value).toBe("3.141");
+	});
+
+	test("lock value input caps at three decimals", async () => {
+		const ui = mount();
+		await setBlock(ui, "drive", 10);
+		await setBlock(ui, "shields", 5);
+		await setBlock(ui, "cargo", 5);
+		await fireEvent.click(ui.getByTestId("calculator-lock-attack"));
+		const lock = ui.getByTestId(
+			"calculator-locked-attack",
+		) as HTMLInputElement;
+		await fireEvent.input(lock, { target: { value: "0.1234" } });
+		expect(lock.value).toBe("0.123");
+	});
+
+	test("ship-block input caps at three decimals", async () => {
+		const ui = mount();
+		const drive = ui.getByTestId("calculator-block-drive") as HTMLInputElement;
+		await fireEvent.input(drive, { target: { value: "1.2345" } });
+		expect(drive.value).toBe("1.234");
+	});
+
+	test("lock spinner step is replaced by ArrowUp/ArrowDown (±0.001)", async () => {
+		const ui = mount();
+		await setBlock(ui, "drive", 10);
+		await setBlock(ui, "shields", 5);
+		await setBlock(ui, "cargo", 5);
+		await fireEvent.click(ui.getByTestId("calculator-lock-attack"));
+		const locked = ui.getByTestId(
+			"calculator-locked-attack",
+		) as HTMLInputElement;
+		// Lock value is seeded from outputs.attack (0 with no weapons).
+		const start = Number(locked.value);
+		locked.focus();
+		await fireEvent.keyDown(locked, { key: "ArrowUp" });
+		expect(Number(locked.value)).toBeCloseTo(start + 0.001, 9);
+		await fireEvent.keyDown(locked, { key: "ArrowDown" });
+		expect(Number(locked.value)).toBeCloseTo(start, 9);
+	});
+
+	test("flags the lock as infeasible when the back-solved block falls in (0, 1)", async () => {
+		// attack lock → weapons = targetAttack / weaponsTech. weaponsTech
+		// is 1.5; a target of 0.5 would force weapons = 0.333… which
+		// fails the DWSC rule (must be 0 or ≥ 1).
+		const ui = mount();
+		await setBlock(ui, "drive", 10);
+		await setBlock(ui, "armament", 2);
+		await setBlock(ui, "weapons", 5);
+		await setBlock(ui, "shields", 5);
+		await setBlock(ui, "cargo", 5);
+		await fireEvent.click(ui.getByTestId("calculator-lock-attack"));
+		await fireEvent.input(ui.getByTestId("calculator-locked-attack"), {
+			target: { value: "0.5" },
+		});
+		const locked = ui.getByTestId("calculator-locked-attack");
+		expect(locked).toHaveAttribute(
+			"title",
+			expect.stringMatching(/cannot be reached/i),
+		);
+		// The claimed block is not back-solved into the invalid (0, 1)
+		// range — the weapons input keeps the user's typed value (5).
+		expect(ui.getByTestId("calculator-block-weapons")).toHaveValue(5);
+	});
+
+	test("dropdown selection loads the class immediately (no blur needed)", async () => {
+		const ui = mount({
+			report: makeReport({
+				localShipClass: [
+					{
+						name: "Scout",
+						drive: 3,
+						armament: 0,
+						weapons: 0,
+						shields: 2,
+						cargo: 1,
+					},
+				],
+			} as unknown as GameReport),
+		});
+		// A datalist option click sets the whole value at once — Firefox
+		// reports no `inputType`, Chromium reports "insertReplacementText".
+		// Simulate the latter; the calculator should load before any
+		// `change` event.
+		await fireEvent.input(ui.getByTestId("calculator-name"), {
+			target: { value: "Scout" },
+			inputType: "insertReplacementText",
+		});
+		expect(ui.getByTestId("calculator-block-drive")).toHaveValue(3);
+		expect(ui.getByTestId("calculator-block-shields")).toHaveValue(2);
+	});
+
+	test("dropdown selection asks before discarding manual edits", async () => {
+		const ui = mount({
+			report: makeReport({
+				localShipClass: [
+					{
+						name: "Scout",
+						drive: 3,
+						armament: 0,
+						weapons: 0,
+						shields: 2,
+						cargo: 1,
+					},
+				],
+			} as unknown as GameReport),
+		});
+		// The user has hand-edited the design.
+		await setBlock(ui, "drive", 7);
+		const confirm = vi.spyOn(window, "confirm").mockReturnValue(false);
+		await fireEvent.input(ui.getByTestId("calculator-name"), {
+			target: { value: "Scout" },
+			inputType: "insertReplacementText",
+		});
+		expect(confirm).toHaveBeenCalledTimes(1);
+		// The user said no — the manual edits stay.
+		expect(ui.getByTestId("calculator-block-drive")).toHaveValue(7);
+		// The name field is reverted to the previously loaded class (or
+		// empty), so the field does not pretend the load happened.
+		expect(ui.getByTestId("calculator-name")).toHaveValue("");
+
+		confirm.mockReturnValue(true);
+		await fireEvent.input(ui.getByTestId("calculator-name"), {
+			target: { value: "Scout" },
+			inputType: "insertReplacementText",
+		});
+		// Confirmed — the class is now loaded.
+		expect(ui.getByTestId("calculator-block-drive")).toHaveValue(3);
+		confirm.mockRestore();
+	});
+
+	test("dropdown selection loads silently when the design is clean", async () => {
+		const ui = mount({
+			report: makeReport({
+				localShipClass: [
+					{
+						name: "Scout",
+						drive: 3,
+						armament: 0,
+						weapons: 0,
+						shields: 2,
+						cargo: 1,
+					},
+				],
+			} as unknown as GameReport),
+		});
+		const confirm = vi.spyOn(window, "confirm");
+		await fireEvent.input(ui.getByTestId("calculator-name"), {
+			target: { value: "Scout" },
+			inputType: "insertReplacementText",
+		});
+		expect(confirm).not.toHaveBeenCalled();
+		expect(ui.getByTestId("calculator-block-drive")).toHaveValue(3);
+		confirm.mockRestore();
+	});
+
+	test("does not render a delete-class button after loading a class", async () => {
+		const ui = mount({
+			report: makeReport({
+				localShipClass: [
+					{
+						name: "Scout",
+						drive: 3,
+						armament: 0,
+						weapons: 0,
+						shields: 2,
+						cargo: 1,
+					},
+				],
+			} as unknown as GameReport),
+		});
+		await fireEvent.input(ui.getByTestId("calculator-name"), {
+			target: { value: "Scout" },
+			inputType: "insertReplacementText",
+		});
+		// The loaded class state used to render a `delete <name>` button;
+		// the calculator no longer owns delete-class — issue #53 will.
+		expect(ui.queryByTestId("calculator-delete")).toBeNull();
+	});
+
+	test("bombing and cargo-capacity rows reserve the lock slot for column alignment", () => {
+		const ui = mount();
+		for (const id of ["calculator-out-bombing", "calculator-out-cargo-capacity"]) {
+			const cell = ui.getByTestId(id).parentElement;
+			expect(cell).not.toBeNull();
+			// A hidden placeholder occupies the same width as the lock button
+			// on the mass/speed/attack/defence rows, so the value column does
+			// not drift right on the rows without a lock.
+			expect(cell!.querySelector(".lock-slot")).not.toBeNull();
+		}
+	});
 });
diff --git a/ui/frontend/tests/e2e/game-shell-inspector.spec.ts b/ui/frontend/tests/e2e/game-shell-inspector.spec.ts
index 0fa9a18..3bc37e1 100644
--- a/ui/frontend/tests/e2e/game-shell-inspector.spec.ts
+++ b/ui/frontend/tests/e2e/game-shell-inspector.spec.ts
@@ -275,6 +275,9 @@ test("calculator draws reach circles for the selected planet", async ({
 	await calc.getByTestId("calculator-block-drive").fill("10");
 	await calc.getByTestId("calculator-block-shields").fill("5");
 	await calc.getByTestId("calculator-block-cargo").fill("5");
+	// Tech defaults render as a number + open lock; click to reveal the
+	// input before typing an override (the F8-06 unified lock idiom).
+	await calc.getByTestId("calculator-tech-override-drive").click();
 	await calc.getByTestId("calculator-tech-drive").fill("1.2");
 
 	await expect.poll(() => countReachCircles(page)).toBeGreaterThan(0);
diff --git a/ui/frontend/tests/fake-core.ts b/ui/frontend/tests/fake-core.ts
index 61a231d..1b966b2 100644
--- a/ui/frontend/tests/fake-core.ts
+++ b/ui/frontend/tests/fake-core.ts
@@ -94,10 +94,13 @@ export function makeFakeCore(overrides: Partial<Core> = {}): Core {
 		weaponsForAttack: ({ targetAttack, weaponsTech }) =>
 			weaponsTech <= 0 || targetAttack < 0 ? null : targetAttack / weaponsTech,
 		driveForSpeed: ({ targetSpeed, driveTech, restMass }) => {
+			if (driveTech <= 0 || targetSpeed <= 0) return null;
 			const ceiling = 20 * driveTech;
-			if (driveTech <= 0 || targetSpeed <= 0 || targetSpeed >= ceiling) {
-				return null;
+			if (restMass <= 0) {
+				if (targetSpeed !== ceiling) return null;
+				return 1;
 			}
+			if (targetSpeed >= ceiling) return null;
 			return (targetSpeed * restMass) / (ceiling - targetSpeed);
 		},
 		shieldsForDefence: ({ targetDefence, shieldsTech, restMass }) => {