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diff --git a/docs/overnight/polish/speedo-lamps-and-focus.webp b/docs/overnight/polish/speedo-lamps-and-focus.webp
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diff --git a/docs/overnight/polish/speedo-reduced-motion-bay.webp b/docs/overnight/polish/speedo-reduced-motion-bay.webp
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diff --git a/scripts/lib/bundle-budgets.mjs b/scripts/lib/bundle-budgets.mjs
index 155fd47..9d920fd 100644
--- a/scripts/lib/bundle-budgets.mjs
+++ b/scripts/lib/bundle-budgets.mjs
@@ -48,6 +48,8 @@ export const classifyArtifact = (path, source = '') => {
   if (/^assets\/traffic-pass-[^/]+\.js$/u.test(path)) return 'deferred-non-video';
   // PARKING LIGHTS: the favicon renderer, loaded after mount.
   if (/^assets\/tab-icon-[^/]+\.js$/u.test(path)) return 'deferred-non-video';
+  // SPEEDOMETER: the gantry dial's model and DOM driver, loaded after mount.
+  if (/^assets\/speedometer-dial-[^/]+\.js$/u.test(path)) return 'deferred-non-video';
   if (/^assets\/nightdrive-(?:grand-tourer|districts)-[^/]+\.glb$/u.test(path)) return 'first-live-scene';
   if (/\.(?:woff2?|ttf|otf)$/u.test(path)) return 'initial-fonts';
   if (/^assets\/hero-[^/]+\.(?:avif|webp|png|jpe?g)$/u.test(path)) return 'hero-poster';
diff --git a/src/components/AppShell.vue b/src/components/AppShell.vue
index b11e01d..cb1441f 100644
--- a/src/components/AppShell.vue
+++ b/src/components/AppShell.vue
@@ -317,6 +317,10 @@ onUnmounted(() => removePageListeners());
       :resume-id="resume?.id"
       :allow-motion="motion.policy.value.allowSceneRequest"
       :on-section-link-click="navigation.onSectionLinkClick"
+      :frames="journeyBinding"
+      :navigation="navigation.state.value"
+      :sample-beam="headlight.sampleBeam"
+      :animated="motion.policy.value.reason === 'full'"
     />
   </header>
 
diff --git a/src/components/SiteNavigation.vue b/src/components/SiteNavigation.vue
index 9993ac7..e825372 100644
--- a/src/components/SiteNavigation.vue
+++ b/src/components/SiteNavigation.vue
@@ -2,6 +2,10 @@
 import { computed, onBeforeUnmount, onMounted, ref, watch } from "vue";
 import type { SectionId } from "@/content/types";
 import type { JourneySnapshot } from "@/journey/types";
+import type { NavigationState } from "@/journey/navigation-controller";
+import type { BeamSample } from "@/journey/headlight-beam";
+import type { JourneySectionsBinding } from "@/composables/useJourneySections";
+import { useSpeedometer } from "@/composables/useSpeedometer";
 import { SIGN_ACCENTS } from "@/journey/sign-routes";
 
 const props = defineProps<{
@@ -13,6 +17,12 @@ const props = defineProps<{
   /** A returning visitor's last exit: the window offers it from the start. */
   resumeId?: SectionId | undefined;
   onSectionLinkClick: (event: MouseEvent, requestSign?: boolean) => void;
+  /** SPEEDOMETER (left bay): the journey's frame loop, the navigator and the beam. */
+  frames: Pick<JourneySectionsBinding, "requestFrame" | "subscribeFrame">;
+  navigation: NavigationState;
+  sampleBeam: (now: number) => BeamSample | null;
+  /** False snaps the needle: reduced motion, or motion paused. */
+  animated?: boolean;
 }>();
 
 const navigationLabels: Readonly<Record<SectionId, string>> = {
@@ -128,6 +138,31 @@ const driveOn = (): void => {
   list.value?.querySelectorAll<HTMLAnchorElement>("a")[nextIndex.value]?.click();
 };
 
+/* SPEEDOMETER: a 240-degree dial and a digital readout in the left bay,
+   driven by the drive (journey/speedometer.ts). Hover or focus names the
+   route, the exit and the time on the road; a click switches km/h and mph. */
+const speedo = ref<HTMLElement | null>(null);
+const speedometer = useSpeedometer({
+  root: speedo,
+  navigation: () => props.navigation,
+  frames: props.frames,
+  sampleBeam: (now) => props.sampleBeam(now),
+  animated: () => props.animated === true,
+  motionAllowed: () => props.allowMotion === true,
+  detail: () => {
+    const next = props.items[activeIndex.value + 1];
+    const route = `ROUTE ${Math.round(Math.min(1, Math.max(0, props.journey.routeProgress)) * 100)}%`;
+    const exit = `EXIT ${exitNumber(activeIndex.value)}/${exitNumber(props.items.length - 1)}`;
+    const ahead = next === undefined
+      ? "END OF ROUTE"
+      : `NEXT ${exitNumber(activeIndex.value + 1)} ${navigationLabels[next.id]}`.toUpperCase();
+    return `${route} \u00b7 ${exit} \u00b7 ${ahead}`;
+  },
+});
+const speedoLabel = computed(() => (speedometer.units.value === "mph"
+  ? "Speedometer in miles per hour. Switch to kilometres per hour"
+  : "Speedometer in kilometres per hour. Switch to miles per hour"));
+
 const navigate = (event: MouseEvent): void => {
   props.onSectionLinkClick(event, true);
   if (window.matchMedia("(max-width: 767px)").matches)
@@ -137,6 +172,37 @@ const navigate = (event: MouseEvent): void => {
 
 <template>
   <nav class="site-navigation" aria-label="Portfolio sections" :data-enhanced="enhanced" :data-docked="docked" :data-motion="allowMotion === true" :style="{ '--nav-rest-scale': restScale, '--route-index': activeIndex, '--route-count': items.length, '--sign-accent': SIGN_ACCENTS[items[activeIndex]?.id ?? 'start'] }">
+    <button
+      ref="speedo"
+      type="button"
+      class="speedo"
+      :aria-label="speedoLabel"
+      data-engine="off"
+      @click="speedometer.toggleUnits"
+      @pointerenter="speedometer.setDetail(true)"
+      @pointerleave="speedometer.setDetail(false)"
+      @focus="speedometer.setDetail(true)"
+      @blur="speedometer.setDetail(false)"
+    >
+      <svg class="speedo__dial" viewBox="0 0 64 46" aria-hidden="true" focusable="false">
+        <path class="speedo__track" d="M11.2 42A24 24 0 1 1 52.8 42" pathLength="100" />
+        <path class="speedo__redline" d="M11.2 42A24 24 0 1 1 52.8 42" pathLength="100" />
+        <path class="speedo__glow" d="M11.2 42A24 24 0 1 1 52.8 42" pathLength="100" />
+        <path class="speedo__fill" d="M11.2 42A24 24 0 1 1 52.8 42" pathLength="100" />
+        <!-- Ticks every 20 km/h over the 240-degree sweep, major every 40. -->
+        <path class="speedo__ticks" d="M10.8 33.7L8.4 34.2M13.4 19.2L11.2 18.0M24.6 9.8L23.8 7.4M39.4 9.8L40.2 7.4M50.6 19.2L52.8 18.0M53.2 33.7L55.6 34.2" />
+        <path class="speedo__ticks" data-major d="M16.0 39.2L11.2 42.0M13.8 26.8L8.4 25.8M20.1 15.8L16.6 11.6M32.0 11.5L32.0 6.0M43.9 15.8L47.4 11.6M50.2 26.8L55.6 25.8M48.0 39.2L52.8 42.0" />
+        <g class="speedo__needle"><line x1="32" y1="33" x2="32" y2="9" /></g>
+        <circle class="speedo__hub" cx="32" cy="30" r="2.4" />
+      </svg>
+      <span class="speedo__readout" aria-hidden="true">
+        <span class="speedo__digits">000</span>
+        <span class="speedo__unit">{{ speedometer.units.value === 'mph' ? 'MPH' : 'KM/H' }}</span>
+        <span class="speedo__lamp"></span>
+        <span class="speedo__line">TRIP <span class="speedo__trip">000.0</span><span class="speedo__gear">P</span></span>
+      </span>
+      <span class="speedo__detail" aria-hidden="true" data-detail=""></span>
+    </button>
     <details ref="disclosure" class="site-navigation__disclosure" open>
       <summary :data-exit="exitNumber(activeIndex)" :data-label="navigationLabels[items[activeIndex]?.id ?? 'start']">Navigate</summary>
       <ul ref="list">
diff --git a/src/composables/useSpeedometer.ts b/src/composables/useSpeedometer.ts
new file mode 100644
index 0000000..0ef47d1
--- /dev/null
+++ b/src/composables/useSpeedometer.ts
@@ -0,0 +1,90 @@
+import { onMounted, onUnmounted, ref, type Ref } from 'vue';
+import type { BeamSample } from '@/journey/headlight-beam';
+import type { NavigationState } from '@/journey/navigation-controller';
+import type { SpeedometerDial } from '@/journey/speedometer-dial';
+import type { SpeedUnits } from '@/journey/speedometer';
+import type { JourneySnapshot } from '@/journey/types';
+
+const UNITS_KEY = 'nightdrive:units';
+
+export interface SpeedometerSources {
+  /** The gauge button; its readouts are found by class, after mount. */
+  root: Ref<HTMLElement | null>;
+  navigation: () => NavigationState;
+  /** The journey's frame loop: the gauge rides it instead of its own rAF. */
+  frames: {
+    requestFrame(): void;
+    subscribeFrame(listener: (now: number, snapshot: JourneySnapshot) => boolean): () => void;
+  };
+  sampleBeam: (now: number) => BeamSample | null;
+  animated: () => boolean;
+  motionAllowed: () => boolean;
+  detail: () => string;
+}
+
+export interface SpeedometerBinding {
+  units: Ref<SpeedUnits>;
+  toggleUnits(): void;
+  setDetail(on: boolean): void;
+}
+
+/**
+ * SPEEDOMETER: the gauge in the gantry's left bay. The model and the DOM
+ * driver are a lazy chunk (journey/speedometer-dial.ts) fetched after mount;
+ * until it lands the server-rendered dial reads engine off, which is where
+ * the ignition starts anyway. This side keeps the units preference and
+ * hands the driver the journey's frame loop.
+ */
+export function useSpeedometer(sources: SpeedometerSources): SpeedometerBinding {
+  const units = ref<SpeedUnits>('kmh');
+  let dial: SpeedometerDial | null = null;
+  let detailOn = false;
+  let mounted = false;
+  let unsubscribe = (): void => {};
+
+  onMounted(() => {
+    const el = sources.root.value;
+    if (!el) return;
+    mounted = true;
+    try {
+      units.value = window.localStorage.getItem(UNITS_KEY) === 'mph' ? 'mph' : 'kmh';
+    } catch {
+      // No memory: km/h.
+    }
+    import('@/journey/speedometer-dial').then((module) => {
+      if (!mounted) return;
+      dial = module.createSpeedometerDial(el, {
+        ...sources,
+        units: () => units.value,
+        kick: () => sources.frames.requestFrame(),
+      });
+      dial.setDetail(detailOn);
+      unsubscribe = sources.frames.subscribeFrame(dial.frame);
+      sources.frames.requestFrame();
+    }, () => {});
+  });
+
+  onUnmounted(() => {
+    mounted = false;
+    unsubscribe();
+    dial?.dispose();
+    dial = null;
+  });
+
+  return {
+    units,
+    toggleUnits() {
+      units.value = units.value === 'mph' ? 'kmh' : 'mph';
+      try {
+        window.localStorage.setItem(UNITS_KEY, units.value);
+      } catch {
+        // A preference, not a record.
+      }
+      sources.frames.requestFrame();
+    },
+    setDetail(on) {
+      detailOn = on;
+      dial?.setDetail(on);
+    },
+  };
+}
diff --git a/src/journey/speedometer-dial.ts b/src/journey/speedometer-dial.ts
new file mode 100644
index 0000000..7bb4a72
--- /dev/null
+++ b/src/journey/speedometer-dial.ts
@@ -0,0 +1,150 @@
+/**
+ * SPEEDOMETER, DOM side (a lazy chunk with the model: nothing of it is in
+ * the initial bundle). Each journey frame steps the pure model and writes
+ * only what changed: --needle/--speed/--throttle on the gauge, data-engine,
+ * data-brake, data-jump and data-flash, and the digit, gear, trip and detail
+ * text. The frame keeps the journey loop running while the needle settles,
+ * during a flash and for the ignition sweep; otherwise scroll events and the
+ * navigator drive it. Below 1280 the bay is the summary's and the gauge is
+ * display: none, so the frame does nothing there.
+ */
+import type { BeamSample } from '@/journey/headlight-beam';
+import { readIgnition } from '@/journey/ignition-feed';
+import type { NavigationState } from '@/journey/navigation-controller';
+import {
+  createBeamFlashDetector,
+  createSpeedometerModel,
+  formatSpeed,
+  formatTrip,
+  needleDegrees,
+  MAX_KMH,
+  type SpeedometerInput,
+  type SpeedUnits,
+} from '@/journey/speedometer';
+import type { JourneySnapshot } from '@/journey/types';
+
+/** With a scene on its way the engine waits for the ignition this long at most. */
+const IGNITION_WAIT_MS = 4_000;
+/** After a click the loop runs long enough to see the high beam lift. */
+const FLASH_WATCH_MS = 600;
+
+export interface DialSources {
+  navigation: () => NavigationState;
+  /** HIGH BEAM: the gauge flares with the flash. */
+  sampleBeam: (now: number) => BeamSample | null;
+  /** False snaps the needle (reduced motion, paused). */
+  animated: () => boolean;
+  /** A scene is coming: the engine waits for its ignition. */
+  motionAllowed: () => boolean;
+  units: () => SpeedUnits;
+  /** The hover line (route, exits, next), minus the time on the road. */
+  detail: () => string;
+  /** Asks the journey loop for a frame. */
+  kick: () => void;
+}
+
+export interface SpeedometerDial {
+  frame(now: number, journey: JourneySnapshot): boolean;
+  /** Pointer or focus on the gauge: the detail line follows the drive. */
+  setDetail(on: boolean): void;
+  dispose(): void;
+}
+
+export function createSpeedometerDial(el: HTMLElement, sources: DialSources): SpeedometerDial {
+  const model = createSpeedometerModel();
+  const input: SpeedometerInput = {
+    driveSpeed: 0, direction: 0, acceleration: 0, routeProgress: 0, ignition: 0, jump: false, arrived: false,
+  };
+  const mountedAt = performance.now();
+  const query = window.matchMedia('(min-width: 1280px)');
+  let wide = query.matches;
+  let watchUntil = -Infinity;
+  const flashOf = createBeamFlashDetector();
+  let detailOn = false;
+  // Last written values, so a frame that changes nothing writes nothing.
+  const numbers = [NaN, NaN, NaN];
+  const strings = ['', '', '', '', ''];
+  const flags = [false, false, false];
+
+  const prop = (slot: number, name: string, value: number, epsilon: number, digits: number): void => {
+    if (Math.abs(value - numbers[slot]!) < epsilon) return;
+    numbers[slot] = value;
+    el.style.setProperty(name, value.toFixed(digits));
+  };
+  const text = (slot: number, selector: string, value: string, attribute?: string): void => {
+    if (strings[slot] === value) return;
+    strings[slot] = value;
+    const target = el.querySelector(selector);
+    if (!target) return;
+    if (attribute) target.setAttribute(attribute, value);
+    else target.textContent = value;
+  };
+  const flag = (slot: number, name: string, on: boolean): void => {
+    if (flags[slot] === on) return;
+    flags[slot] = on;
+    el.toggleAttribute(name, on);
+  };
+
+  // The scene writes html[data-ignition] from its first frame; until then
+  // (or for 4 s at most) the engine is off. Landing mid-page skips it.
+  let awaitingIgnition = sources.motionAllowed() && window.location.hash === '';
+  const ignited = (): void => {
+    awaitingIgnition = false;
+    window.clearTimeout(ignitionTimer);
+    sources.kick();
+  };
+  const ignitionTimer = awaitingIgnition ? window.setTimeout(ignited, IGNITION_WAIT_MS) : 0;
+  const observer = new MutationObserver(ignited);
+  observer.observe(document.documentElement, { attributes: true, attributeFilter: ['data-ignition'] });
+  const onQuery = (): void => { wide = query.matches; sources.kick(); };
+  query.addEventListener('change', onQuery);
+  // A click anywhere may flash the high beam: watch the beam for a moment.
+  const onClick = (): void => { watchUntil = performance.now() + FLASH_WATCH_MS; sources.kick(); };
+  document.addEventListener('click', onClick, { passive: true });
+
+  return {
+    frame(now, journey) {
+      if (!wide) return false;
+      const navigation = sources.navigation();
+      input.driveSpeed = journey.driveSpeed;
+      input.direction = journey.direction;
+      input.acceleration = journey.acceleration;
+      input.routeProgress = journey.routeProgress;
+      input.ignition = awaitingIgnition ? 0 : readIgnition().phase;
+      input.jump = navigation.phase === 'travelling' && navigation.source === 'explicit-navigation';
+      input.arrived = journey.arrived;
+      const out = model.step(now, input, sources.animated());
+
+      const beam = sources.sampleBeam(now);
+      const flashing = flashOf(beam === null ? 0 : beam.intensity) && out.engine === 'on';
+
+      const units = sources.units();
+      prop(0, '--needle', needleDegrees(out.kmh), 0.15, 1);
+      prop(1, '--speed', Math.min(1, out.kmh / MAX_KMH), 0.002, 3);
+      prop(2, '--throttle', out.throttle, 0.01, 2);
+      text(0, '.speedo__digits', formatSpeed(out.kmh, units));
+      text(1, '.speedo__gear', out.gear);
+      text(2, '.speedo__trip', formatTrip(out.tripKm, units));
+      const engine = out.engine === 'off' && input.arrived ? 'parked' : out.engine;
+      if (strings[3] !== engine) { strings[3] = engine; el.dataset.engine = engine; }
+      flag(0, 'data-brake', out.brake);
+      flag(1, 'data-jump', input.jump);
+      flag(2, 'data-flash', flashing);
+      if (detailOn) {
+        const minutes = Math.max(1, Math.round((now - mountedAt) / 60_000));
+        text(4, '.speedo__detail', `${sources.detail()} · ${minutes} MIN ON THE ROAD`, 'data-detail');
+      }
+      return !out.settled || flashing || now < watchUntil;
+    },
+    setDetail(on) {
+      detailOn = on;
+      if (on) sources.kick();
+    },
+    dispose() {
+      observer.disconnect();
+      query.removeEventListener('change', onQuery);
+      document.removeEventListener('click', onClick);
+      window.clearTimeout(ignitionTimer);
+    },
+  };
+}
diff --git a/src/journey/speedometer.ts b/src/journey/speedometer.ts
new file mode 100644
index 0000000..5d83f7f
--- /dev/null
+++ b/src/journey/speedometer.ts
@@ -0,0 +1,178 @@
+/**
+ * SPEEDOMETER: the instrument in the gantry's left bay. Pure: the drive
+ * state (driveSpeed, direction, acceleration, route progress), the scene's
+ * ignition phase and the navigator's state map to a target speed; a light
+ * underdamped spring carries the needle there (a rev overshoot, a settle),
+ * and the readouts (digits, gear, trip) derive from the needle. Nothing here
+ * touches the DOM or allocates per step: the frame object is reused.
+ */
+
+export type SpeedUnits = 'kmh' | 'mph';
+/** off: before ignition / parked. lamps: backlight on, needle at rest.
+ * on: driving. */
+export type EngineState = 'off' | 'lamps' | 'on';
+
+/** Idle cruise reads 88 km/h; the fastest scroll pins the needle at 240. */
+export const CRUISE_KMH = 88;
+export const MAX_KMH = 240;
+/** Scrolling back is braking: full reverse throttle reads 34 km/h. */
+export const BRAKE_KMH = 34;
+/** The route end to end, for the trip odometer. */
+export const ROUTE_KM = 48;
+export const KMH_PER_MPH = 1.609344;
+/** The idle drive speed of the scroll controller (scroll-drive-controller.ts). */
+export const CRUISE_DRIVE = 0.18;
+/** The needle sweeps 240 degrees, from 8 o'clock over the top to 4 o'clock. */
+export const NEEDLE_SWEEP_DEG = 240;
+/** Ignition self-test: the needle sweeps to full scale, then falls to cruise. */
+export const SWEEP_MS = 720;
+/** Gear thresholds (km/h) for the shift indicator. */
+const GEARS: readonly number[] = [6, 30, 55, 85, 120, 170];
+
+export interface SpeedometerInput {
+  driveSpeed: number;
+  direction: -1 | 0 | 1;
+  acceleration: number;
+  routeProgress: number;
+  /** The scene's ignition phase (ignition-feed.ts): 0 cold, 1 lamps, 2 rolling, 3 driving. */
+  ignition: 0 | 1 | 2 | 3;
+  /** An explicit navigation in flight: overdrive. */
+  jump: boolean;
+  /** Parked at the destination: engine off. */
+  arrived: boolean;
+}
+
+export interface SpeedometerFrame {
+  /** The needle, km/h. */
+  kmh: number;
+  target: number;
+  engine: EngineState;
+  brake: boolean;
+  /** 0..1, how hard the drive is pushing (lights the arc). */
+  throttle: number;
+  gear: string;
+  tripKm: number;
+  /** Nothing moves until the input changes. */
+  settled: boolean;
+}
+
+export interface SpeedometerModel {
+  /** Advance to `now` (ms). `animated` false snaps the needle to its target. */
+  step(now: number, input: SpeedometerInput, animated: boolean): SpeedometerFrame;
+}
+
+const clamp01 = (v: number): number => (v > 0 ? (v < 1 ? v : 1) : 0);
+
+export const isBraking = (input: Pick<SpeedometerInput, 'direction' | 'acceleration'>): boolean =>
+  input.direction === -1 && input.acceleration > 0.04;
+
+/** Where the needle wants to be, km/h. */
+export function speedTargetKmh(input: SpeedometerInput): number {
+  if (input.arrived || input.ignition < 2) return 0;
+  if (input.jump) return MAX_KMH;
+  const push = clamp01((input.driveSpeed - CRUISE_DRIVE) / (1 - CRUISE_DRIVE));
+  if (isBraking(input)) return CRUISE_KMH - (CRUISE_KMH - BRAKE_KMH) * clamp01(input.acceleration);
+  return CRUISE_KMH + (MAX_KMH - CRUISE_KMH) * push;
+}
+
+export function engineStateFor(input: Pick<SpeedometerInput, 'ignition' | 'arrived'>): EngineState {
+  if (input.arrived) return 'off';
+  return input.ignition === 0 ? 'off' : input.ignition === 1 ? 'lamps' : 'on';
+}
+
+/** Needle rotation in degrees (0 at 12 o'clock, clockwise positive). */
+export const needleDegrees = (kmh: number): number =>
+  -NEEDLE_SWEEP_DEG / 2 + NEEDLE_SWEEP_DEG * clamp01(kmh / MAX_KMH);
+
+export function gearFor(kmh: number, engine: EngineState): string {
+  if (engine !== 'on') return 'P';
+  let gear = 0;
+  for (const threshold of GEARS) if (kmh >= threshold) gear += 1;
+  return gear === 0 ? 'N' : String(gear);
+}
+
+export const tripKmFor = (routeProgress: number): number => ROUTE_KM * clamp01(routeProgress);
+
+export const toUnits = (kmh: number, units: SpeedUnits): number =>
+  units === 'mph' ? kmh / KMH_PER_MPH : kmh;
+
+/** Three digits for the readout: "088". A rev overshoot stays on the dial. */
+export const formatSpeed = (kmh: number, units: SpeedUnits): string =>
+  String(Math.round(toUnits(Math.min(MAX_KMH, Math.max(0, kmh)), units))).padStart(3, '0');
+
+/** "012.4" for the trip odometer. */
+export const formatTrip = (km: number, units: SpeedUnits): string =>
+  Math.max(0, toUnits(km, units)).toFixed(1).padStart(5, '0');
+
+export const unitLabel = (units: SpeedUnits): string => (units === 'mph' ? 'MPH' : 'KM/H');
+
+/** Spring: omega 7.5 rad/s (a 0.84 s period on the overshoot), zeta 0.62. */
+const OMEGA = 7.5;
+const ZETA = 0.62;
+const MAX_STEP_S = 0.05;
+const SETTLE_KMH = 0.25;
+const SETTLE_RATE = 2;
+
+export function createSpeedometerModel(): SpeedometerModel {
+  let kmh = 0;
+  let rate = 0;
+  let last: number | null = null;
+  let sweepUntil = -Infinity;
+  let previousEngine: EngineState = 'off';
+  const frame: SpeedometerFrame = {
+    kmh: 0, target: 0, engine: 'off', brake: false, throttle: 0, gear: 'P', tripKm: 0, settled: false,
+  };
+
+  return {
+    step(now, input, animated) {
+      const engine = engineStateFor(input);
+      // The engine coming on runs the self-test sweep (not under reduced motion).
+      if (engine === 'on' && previousEngine !== 'on' && animated) sweepUntil = now + SWEEP_MS;
+      previousEngine = engine;
+      const target = now < sweepUntil ? MAX_KMH : speedTargetKmh(input);
+      const dt = last === null ? 0 : Math.min(MAX_STEP_S, Math.max(0, (now - last) / 1000));
+      last = now;
+      if (!animated) {
+        kmh = target;
+        rate = 0;
+      } else if (dt > 0) {
+        // Semi-implicit Euler on x'' = -w^2 (x - t) - 2 z w x'.
+        rate += (-OMEGA * OMEGA * (kmh - target) - 2 * ZETA * OMEGA * rate) * dt;
+        kmh += rate * dt;
+        if (kmh < 0) { kmh = 0; rate = 0; }
+        if (Math.abs(kmh - target) < SETTLE_KMH && Math.abs(rate) < SETTLE_RATE) {
+          kmh = target;
+          rate = 0;
+        }
+      }
+      frame.kmh = kmh;
+      frame.target = target;
+      frame.engine = engine;
+      frame.brake = engine === 'on' && !input.jump && isBraking(input);
+      frame.throttle = engine === 'on' ? (input.jump ? 1 : clamp01(input.acceleration)) : 0;
+      frame.gear = gearFor(kmh, engine);
+      frame.tripKm = tripKmFor(input.routeProgress);
+      frame.settled = kmh === target && rate === 0 && now >= sweepUntil;
+      return frame;
+    },
+  };
+}
+
+/**
+ * HIGH BEAM: a flash is a fast lift of the beam to 1 from its 0.72 rest. The
+ * detector arms on a steady or falling reading at rest level (0.3 to 0.85),
+ * so neither the dark beam before the scene nor the intro sweep (0 to 1,
+ * rising) reads as a flash, and it holds while the beam stays above 0.95.
+ */
+export function createBeamFlashDetector(): (intensity: number) => boolean {
+  let armed = false;
+  let last = 0;
+  let on = false;
+  return (intensity) => {
+    if (intensity > 0.3 && intensity < 0.85 && intensity <= last + 1e-3) armed = true;
+    last = intensity;
+    if (on) on = intensity > 0.95;
+    else if (armed && intensity > 0.95) { on = true; armed = false; }
+    return on;
+  };
+}
diff --git a/src/styles/gantry.css b/src/styles/gantry.css
index 7076bf3..a9f29e4 100644
--- a/src/styles/gantry.css
+++ b/src/styles/gantry.css
@@ -98,8 +98,227 @@ html .site-navigation[data-enhanced='true'][data-docked='true']::before {
   mask-composite: exclude, add;
 }
 
-/* No brand plate in the left bay: the hero carries the name (owner's call:
-   a name in the nav bar read as self-promotion). */
+/* ---------- SPEEDOMETER in the left bay ----------
+   No brand plate here (owner's call: a name in the nav bar read as
+   self-promotion). Instead the dash's instrument: a 240-degree dial whose
+   arc fills in the chapter's sign colour, a needle on a light spring
+   (useSpeedometer writes --needle, --speed, --throttle and the data-* states
+   per journey frame), a three-digit readout, the trip odometer and a gear.
+   Wide only: below 1280 the bay is the summary's, and the dial is gone. */
+.speedo {
+  --dial-ink: #bfaed3;
+  --dial-lit: #f4e6ff;
+  position: absolute;
+  z-index: 1;
+  inset: 0 auto 0 16px;
+  display: grid;
+  grid-template-columns: 64px minmax(0, 1fr);
+  align-items: center;
+  column-gap: 8px;
+  inline-size: calc(var(--bay-l) - 28px);
+  margin: 0;
+  padding: 0 4px;
+  border: 0;
+  border-radius: 0;
+  background: none;
+  color: var(--dial-ink);
+  font: 650 0.6rem/1 var(--mono);
+  letter-spacing: 0.1em;
+  text-align: start;
+  cursor: pointer;
+  -webkit-user-select: none;
+  user-select: none;
+}
+.speedo:focus-visible {
+  outline: 2px solid var(--focus);
+  outline-offset: -6px;
+}
+.speedo__dial {
+  display: block;
+  inline-size: 64px;
+  block-size: 46px;
+  overflow: visible;
+  fill: none;
+  stroke-linecap: round;
+}
+.speedo__track {
+  stroke: rgb(217 200 244 / 16%);
+  stroke-width: 3;
+}
+/* The top fifth of the scale (192-240) is the redline. */
+.speedo__redline {
+  stroke: rgb(255 93 122 / 55%);
+  stroke-width: 3;
+  stroke-dasharray: 20 100;
+  stroke-dashoffset: -80;
+}
+.speedo__fill,
+.speedo__glow {
+  stroke: var(--sign-accent, #ff83c2);
+  stroke-width: 3;
+  stroke-dasharray: 100;
+  stroke-dashoffset: calc(100 - var(--speed, 0) * 100);
+  transition: stroke 480ms ease;
+}
+.speedo__glow {
+  stroke-width: 7;
+  opacity: calc(0.25 + var(--throttle, 0) * 0.6);
+  filter: blur(3px);
+}
+.speedo__ticks {
+  stroke: rgb(217 200 244 / 32%);
+  stroke-width: 1;
+}
+.speedo__ticks[data-major] {
+  stroke: rgb(217 200 244 / 55%);
+  stroke-width: 1.4;
+}
+.speedo__needle {
+  stroke: var(--focus);
+  stroke-width: 2;
+  transform-box: view-box;
+  transform-origin: 32px 30px;
+  transform: rotate(calc(var(--needle, -120) * 1deg));
+  filter: drop-shadow(0 0 2px rgb(255 214 147 / 70%));
+}
+.speedo__hub {
+  fill: #170e29;
+  stroke: var(--focus);
+  stroke-width: 1.2;
+}
+.speedo__readout {
+  display: grid;
+  grid-template-columns: auto minmax(0, 1fr);
+  grid-template-rows: auto auto;
+  align-items: baseline;
+  column-gap: 6px;
+  row-gap: 5px;
+  min-inline-size: 0;
+}
+.speedo__digits {
+  color: var(--dial-lit);
+  font-size: 1.3rem;
+  font-weight: 560;
+  font-variant-numeric: tabular-nums;
+  letter-spacing: 0.04em;
+  text-shadow: 0 0 10px color-mix(in srgb, var(--sign-accent, #ff83c2) calc(var(--throttle, 0) * 90%), transparent);
+}
+.speedo__unit,
+.speedo__lamp {
+  grid-area: 1 / 2;
+  font-size: 0.5rem;
+  letter-spacing: 0.14em;
+  white-space: nowrap;
+  transition: opacity 120ms ease;
+}
+.speedo__unit { opacity: 0.8; }
+/* The warning lamp takes the unit's place: BRAKE on a reverse scroll,
+   OVERDRIVE on a navigator jump, ENGINE OFF once parked. */
+.speedo__lamp {
+  font-size: 0.46rem;
+  opacity: 0;
+}
+.speedo:is([data-brake], [data-jump], [data-engine='parked']) .speedo__unit { opacity: 0; transition-duration: 0ms; }
+.speedo__lamp::before { content: '' / ''; }
+.speedo[data-brake] .speedo__lamp,
+.speedo[data-jump] .speedo__lamp,
+.speedo[data-engine='parked'] .speedo__lamp { opacity: 1; }
+.speedo[data-brake] .speedo__lamp { color: #ff8da4; }
+.speedo[data-brake] .speedo__lamp::before { content: 'BRAKE' / ''; }
+.speedo[data-jump] .speedo__lamp { color: var(--sign-accent, #ff83c2); }
+.speedo[data-jump] .speedo__lamp::before { content: 'OVERDRIVE' / ''; }
+.speedo[data-engine='parked'] .speedo__lamp { color: var(--focus); }
+.speedo[data-engine='parked'] .speedo__lamp::before { content: 'ENGINE OFF' / ''; }
+.speedo__line {
+  grid-column: 1 / -1;
+  display: flex;
+  align-items: baseline;
+  gap: 5px;
+  font-size: 0.52rem;
+  letter-spacing: 0.12em;
+  white-space: nowrap;
+}
+.speedo__trip {
+  color: var(--dial-lit);
+  font-variant-numeric: tabular-nums;
+}
+.speedo__gear {
+  margin-inline-start: auto;
+  padding: 2px 4px 1px;
+  border: 1px solid rgb(217 200 244 / 30%);
+  border-radius: 2px;
+  color: var(--dial-lit);
+  font-size: 0.5rem;
+  line-height: 1;
+}
+/* Engine off (cold, or parked at the destination): a dark dial. */
+.speedo[data-engine='off'] .speedo__dial,
+.speedo[data-engine='parked'] .speedo__dial { opacity: 0.45; }
+.speedo[data-engine='off'] .speedo__readout,
+.speedo[data-engine='parked'] .speedo__readout { --dial-lit: #8f7aa6; }
+.speedo[data-engine='parked'] .speedo__digits { color: #c9b8dc; }
+/* Lamps: the backlight warms before the needle sweeps. */
+.speedo[data-engine='lamps'] .speedo__dial { opacity: 0.7; }
+.speedo[data-engine='lamps'] .speedo__digits { color: #e6c89c; }
+.speedo__dial,
+.speedo__readout { transition: opacity 480ms ease; }
+/* HIGH BEAM: the flash lights the whole instrument for its 0.4 s. */
+.speedo::after {
+  content: '' / '';
+  position: absolute;
+  inset: 8px -6px 8px -2px;
+  border-radius: 6px;
+  background: radial-gradient(60% 80% at 30% 50%, rgb(255 236 200 / 22%), transparent 70%);
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 360ms ease;
+}
+.speedo[data-flash]::after {
+  opacity: 1;
+  transition-duration: 90ms;
+}
+.speedo[data-jump] .speedo__fill { stroke: var(--focus); }
+/* Hover or focus: the route line under the bay (decorative). */
+.speedo__detail {
+  position: absolute;
+  inset: calc(100% + 12px) auto auto 4px;
+  translate: 0 -4px;
+  padding: 0.38rem 0.6rem;
+  border: 1px solid rgb(255 214 147 / 45%);
+  border-radius: 3px;
+  background: #170e29;
+  color: #ffe3b8;
+  font: 650 0.64rem/1 var(--mono);
+  letter-spacing: 0.14em;
+  white-space: nowrap;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 160ms ease, translate 320ms cubic-bezier(0.22, 1, 0.36, 1);
+}
+.speedo__detail::before { content: attr(data-detail) / ''; }
+.speedo:is(:hover, :focus-visible) .speedo__detail[data-detail]:not([data-detail='']) {
+  opacity: 1;
+  translate: 0 0;
+}
+@media (max-width: 1279px) {
+  .speedo { display: none; }
+}
+@media (prefers-reduced-motion: reduce) {
+  .speedo__dial,
+  .speedo__readout,
+  .speedo__fill,
+  .speedo__glow,
+  .speedo__lamp,
+  .speedo::after,
+  .speedo__detail { transition: none; }
+}
+@media (forced-colors: active) {
+  .speedo { color: CanvasText; }
+  .speedo__track, .speedo__ticks { stroke: GrayText; }
+  .speedo__fill, .speedo__needle { stroke: Highlight; }
+  .speedo__glow { display: none; }
+  .speedo__detail { border-color: CanvasText; }
+}
 
 /* ---------- Exits on the beam ---------- */
 @media (min-width: 768px) {
diff --git a/tests/performance/budgets.test.ts b/tests/performance/budgets.test.ts
index 1c10b05..e12addd 100644
--- a/tests/performance/budgets.test.ts
+++ b/tests/performance/budgets.test.ts
@@ -73,6 +73,7 @@ describe('release budgets', () => {
     expect(classifyArtifact('assets/DashcamFrame-c.js', 'postcard')).toBe('deferred-non-video');
     expect(classifyArtifact('assets/DashcamFrame-c.css', '.dashcam-frame{}')).toBe('deferred-non-video');
     expect(classifyArtifact('assets/tab-icon-c.js', 'renderTabIcon')).toBe('deferred-non-video');
+    expect(classifyArtifact('assets/speedometer-dial-c.js', 'createSpeedometerDial')).toBe('deferred-non-video');
     expect(() => classifyArtifact('assets/mystery.bin', '')).toThrow(/unclassified/u);
   });
 
diff --git a/tests/unit/speedometer.test.ts b/tests/unit/speedometer.test.ts
new file mode 100644
index 0000000..49806f3
--- /dev/null
+++ b/tests/unit/speedometer.test.ts
@@ -0,0 +1,217 @@
+import { describe, expect, it } from 'vitest';
+import {
+  BRAKE_KMH,
+  CRUISE_DRIVE,
+  CRUISE_KMH,
+  MAX_KMH,
+  ROUTE_KM,
+  SWEEP_MS,
+  createBeamFlashDetector,
+  createSpeedometerModel,
+  engineStateFor,
+  formatSpeed,
+  formatTrip,
+  gearFor,
+  needleDegrees,
+  speedTargetKmh,
+  tripKmFor,
+  type SpeedometerInput,
+} from '@/journey/speedometer';
+
+const driving = (overrides: Partial<SpeedometerInput> = {}): SpeedometerInput => ({
+  driveSpeed: CRUISE_DRIVE,
+  direction: 0,
+  acceleration: 0,
+  routeProgress: 0,
+  ignition: 3,
+  jump: false,
+  arrived: false,
+  ...overrides,
+});
+
+describe('speedTargetKmh', () => {
+  it('reads the idle cruise at the controller cruise speed', () => {
+    expect(speedTargetKmh(driving())).toBe(CRUISE_KMH);
+  });
+  it('pins the needle at full scale for the fastest scroll', () => {
+    expect(speedTargetKmh(driving({ driveSpeed: 1, acceleration: 1, direction: 1 }))).toBe(MAX_KMH);
+  });
+  it('maps the drive speed linearly between cruise and full scale', () => {
+    const half = speedTargetKmh(driving({ driveSpeed: CRUISE_DRIVE + (1 - CRUISE_DRIVE) / 2, direction: 1, acceleration: 0.5 }));
+    expect(half).toBeCloseTo((CRUISE_KMH + MAX_KMH) / 2, 6);
+  });
+  it('brakes on a reverse scroll, down to the brake floor', () => {
+    expect(speedTargetKmh(driving({ driveSpeed: 1, direction: -1, acceleration: 1 }))).toBe(BRAKE_KMH);
+    expect(speedTargetKmh(driving({ driveSpeed: 0.5, direction: -1, acceleration: 0.5 }))).toBeCloseTo((CRUISE_KMH + BRAKE_KMH) / 2, 6);
+  });
+  it('ignores a reverse direction with no real push (a settling sample)', () => {
+    expect(speedTargetKmh(driving({ direction: -1, acceleration: 0.01 }))).toBe(CRUISE_KMH);
+  });
+  it('goes to overdrive on a navigator jump and to zero when parked or before ignition', () => {
+    expect(speedTargetKmh(driving({ jump: true }))).toBe(MAX_KMH);
+    expect(speedTargetKmh(driving({ arrived: true, driveSpeed: 1 }))).toBe(0);
+    expect(speedTargetKmh(driving({ ignition: 0 }))).toBe(0);
+    expect(speedTargetKmh(driving({ ignition: 1 }))).toBe(0);
+    expect(speedTargetKmh(driving({ ignition: 2 }))).toBe(CRUISE_KMH);
+  });
+  it('never leaves the dial', () => {
+    for (const driveSpeed of [-1, 0, 0.1, 2, Number.NaN]) {
+      const target = speedTargetKmh(driving({ driveSpeed, direction: 1, acceleration: 1 }));
+      expect(target).toBeGreaterThanOrEqual(0);
+      expect(target).toBeLessThanOrEqual(MAX_KMH);
+    }
+  });
+});
+
+describe('engineStateFor', () => {
+  it('follows the ignition phase, and parks at the destination', () => {
+    expect(engineStateFor({ ignition: 0, arrived: false })).toBe('off');
+    expect(engineStateFor({ ignition: 1, arrived: false })).toBe('lamps');
+    expect(engineStateFor({ ignition: 2, arrived: false })).toBe('on');
+    expect(engineStateFor({ ignition: 3, arrived: false })).toBe('on');
+    expect(engineStateFor({ ignition: 3, arrived: true })).toBe('off');
+  });
+});
+
+describe('readouts', () => {
+  it('rotates the needle over 240 degrees from 8 to 4 o\'clock', () => {
+    expect(needleDegrees(0)).toBe(-120);
+    expect(needleDegrees(MAX_KMH)).toBe(120);
+    expect(needleDegrees(MAX_KMH / 2)).toBeCloseTo(0, 9);
+    expect(needleDegrees(-50)).toBe(-120);
+    expect(needleDegrees(999)).toBe(120);
+  });
+  it('shifts up through the gears, and parks when the engine is off', () => {
+    expect(gearFor(0, 'on')).toBe('N');
+    expect(gearFor(10, 'on')).toBe('1');
+    expect(gearFor(CRUISE_KMH, 'on')).toBe('4');
+    expect(gearFor(MAX_KMH, 'on')).toBe('6');
+    expect(gearFor(CRUISE_KMH, 'off')).toBe('P');
+    expect(gearFor(CRUISE_KMH, 'lamps')).toBe('P');
+  });
+  it('formats three digits in either unit', () => {
+    expect(formatSpeed(CRUISE_KMH, 'kmh')).toBe('088');
+    expect(formatSpeed(CRUISE_KMH, 'mph')).toBe('055');
+    expect(formatSpeed(0, 'kmh')).toBe('000');
+    expect(formatSpeed(MAX_KMH, 'mph')).toBe('149');
+    expect(formatSpeed(5000, 'kmh')).toBe('240');
+    expect(formatSpeed(-5, 'kmh')).toBe('000');
+  });
+  it('runs the trip odometer along the route', () => {
+    expect(tripKmFor(0)).toBe(0);
+    expect(tripKmFor(0.5)).toBe(ROUTE_KM / 2);
+    expect(tripKmFor(1.7)).toBe(ROUTE_KM);
+    expect(formatTrip(12.44, 'kmh')).toBe('012.4');
+    expect(formatTrip(0, 'kmh')).toBe('000.0');
+    expect(formatTrip(ROUTE_KM, 'mph')).toBe('029.8');
+  });
+});
+
+describe('createSpeedometerModel', () => {
+  const run = (
+    model: ReturnType<typeof createSpeedometerModel>,
+    input: SpeedometerInput,
+    from: number,
+    to: number,
+    animated = true,
+    step = 16,
+  ): number[] => {
+    const trace: number[] = [];
+    for (let now = from; now <= to; now += step) trace.push(model.step(now, input, animated).kmh);
+    return trace;
+  };
+
+  it('starts dark, runs the self-test sweep on ignition, then settles at cruise', () => {
+    const model = createSpeedometerModel();
+    expect(model.step(0, driving({ ignition: 0 }), true)).toMatchObject({ kmh: 0, engine: 'off', gear: 'P', settled: true });
+    expect(model.step(300, driving({ ignition: 1 }), true)).toMatchObject({ kmh: 0, engine: 'lamps', settled: true });
+    const sweep = run(model, driving({ ignition: 2 }), 316, 316 + SWEEP_MS);
+    expect(Math.max(...sweep)).toBeGreaterThan(CRUISE_KMH * 1.6);
+    const settle = run(model, driving(), 316 + SWEEP_MS + 16, 5_000);
+    const last = settle[settle.length - 1];
+    expect(last).toBe(CRUISE_KMH);
+    expect(model.step(5_016, driving(), true)).toMatchObject({ kmh: CRUISE_KMH, gear: '4', settled: true });
+  });
+
+  it('overshoots like a real needle, then comes to rest', () => {
+    const model = createSpeedometerModel();
+    run(model, driving(), 0, 4_000);
+    const push = driving({ driveSpeed: 1, direction: 1, acceleration: 1 });
+    const trace = run(model, push, 4_016, 8_000);
+    const peak = Math.max(...trace);
+    expect(peak).toBeGreaterThan(MAX_KMH);
+    expect(peak).toBeLessThan(MAX_KMH * 1.2);
+    expect(trace[trace.length - 1]).toBe(MAX_KMH);
+    expect(model.step(8_016, push, true)).toMatchObject({ throttle: 1, brake: false, settled: true });
+  });
+
+  it('never reads below zero, even on the fall after a jump', () => {
+    const model = createSpeedometerModel();
+    run(model, driving({ jump: true }), 0, 3_000);
+    const fall = run(model, driving({ arrived: true }), 3_016, 7_000);
+    expect(Math.min(...fall)).toBeGreaterThanOrEqual(0);
+    expect(fall[fall.length - 1]).toBe(0);
+    expect(model.step(7_016, driving({ arrived: true }), true)).toMatchObject({ engine: 'off', gear: 'P', settled: true });
+  });
+
+  it('snaps without a sweep when not animated (reduced motion)', () => {
+    const model = createSpeedometerModel();
+    expect(model.step(0, driving({ ignition: 0 }), false).kmh).toBe(0);
+    const first = model.step(16, driving(), false);
+    expect(first.kmh).toBe(CRUISE_KMH);
+    expect(first.settled).toBe(true);
+    expect(model.step(32, driving({ driveSpeed: 1, direction: 1, acceleration: 1 }), false).kmh).toBe(MAX_KMH);
+  });
+
+  it('lights the brake lamp on a reverse scroll and the throttle on a push', () => {
+    const model = createSpeedometerModel();
+    const brake = model.step(0, driving({ direction: -1, acceleration: 0.6 }), true);
+    expect(brake.brake).toBe(true);
+    expect(brake.throttle).toBeCloseTo(0.6, 6);
+    expect(model.step(16, driving({ direction: 1, acceleration: 0.3 }), true)).toMatchObject({ brake: false, throttle: 0.3 });
+    expect(model.step(32, driving({ direction: -1, acceleration: 0.6, jump: true }), true).brake).toBe(false);
+  });
+
+  it('clamps a long gap between frames to one small step', () => {
+    const model = createSpeedometerModel();
+    model.step(0, driving(), true);
+    const after = model.step(60_000, driving(), true).kmh;
+    expect(after).toBeGreaterThan(0);
+    expect(after).toBeLessThan(CRUISE_KMH);
+  });
+
+  it('reuses one frame object and tolerates non-finite input', () => {
+    const model = createSpeedometerModel();
+    const a = model.step(0, driving(), true);
+    const b = model.step(16, driving({ driveSpeed: Number.NaN, acceleration: Number.NaN, routeProgress: Number.NaN }), true);
+    expect(b).toBe(a);
+    expect(Number.isFinite(b.kmh)).toBe(true);
+    expect(Number.isFinite(b.tripKm)).toBe(true);
+  });
+});
+
+describe('createBeamFlashDetector', () => {
+  const ramp = (from: number, to: number, steps: number): number[] =>
+    Array.from({ length: steps + 1 }, (_, i) => from + ((to - from) * i) / steps);
+
+  it('ignores the intro sweep and its fall to the rest level', () => {
+    const flash = createBeamFlashDetector();
+    const seen = [...ramp(0, 1, 40), ...ramp(1, 0.72, 20)].map(flash);
+    expect(seen.some(Boolean)).toBe(false);
+  });
+
+  it('fires on a lift from rest and holds while the beam is high', () => {
+    const flash = createBeamFlashDetector();
+    for (const v of [...ramp(0, 1, 40), ...ramp(1, 0.72, 20)]) flash(v);
+    const lift = [...ramp(0.72, 1, 6), 1, 1, 1, ...ramp(1, 0.72, 10)].map(flash);
+    expect(lift.filter(Boolean).length).toBeGreaterThanOrEqual(3);
+    expect(lift[lift.length - 1]).toBe(false);
+    // Settled back at rest, the next lift fires again.
+    expect([...ramp(0.72, 1, 6)].map(flash).some(Boolean)).toBe(true);
+  });
+
+  it('does not fire from a dark beam, nor from a lift straight out of the dark', () => {
+    const flash = createBeamFlashDetector();
+    expect([0, 0, 0, 0, ...ramp(0, 1, 5), 1, 1].map(flash).some(Boolean)).toBe(false);
+  });
+});