Counter widget: one to three linked counters are the digits of one number, published on one message in the finest counter's unit (hours and minutes send 07:30 as 450, 07:55 + 5 min carries to 08:00); wraps or stops at the coarsest's min/max. The arithmetic is one pure module, ui/core/counter.ts, with counter.check.ts. A tile steps each counter with a press up and down and publishes once 300 ms after the last; a round face turns the selected counter on the ring (wheel, keys, a drag counted in steps), its arc where that counter stands in its turn, and a press on a counter's digits selects it. Default config is the time picker. Editor rows, widgetIssue, server type and dtype, docs

frontend/src/client/schemas.gen.ts

@@ -4642,7 +4642,7 @@ export const WidgetDefSchema = {
         },
         type: {
             type: 'string',
-            enum: ['stat', 'gauge', 'chart', 'markdown', 'agenda', 'notification', 'bar', 'icon', 'forecast', 'clock', 'media', 'player', 'embed', 'button', 'buttons', 'switch', 'slider', 'input', 'dropdown', 'color'],
+            enum: ['stat', 'gauge', 'chart', 'markdown', 'agenda', 'notification', 'bar', 'icon', 'forecast', 'clock', 'media', 'player', 'embed', 'button', 'buttons', 'switch', 'slider', 'input', 'dropdown', 'color', 'counter'],
             title: 'Type'
         },
         title: {
@@ -4694,7 +4694,13 @@ The first two are a \`\`list\`\` message, the third a \`\`str\`\`, which is what
 
 A slider may also show what it is setting: \`\`reading\`\` binds
 \`\`{message, dtype, label}\`\` — a room's temperature beside its setpoint —
-held to the same numbers its target is.`
+held to the same numbers its target is.
+
+A counter publishes one number to its target, of which its \`\`counters\`\`
+are the digits: up to three \`\`{label, step, size, min, max}\`\`, coarsest
+first, so hours and minutes publish 07:30 as 450. \`\`wrap\`\` says whether it
+wraps round at its ends; \`\`docs/interface/dashboards.md\`\` has the
+arithmetic.`
 } as const;
 
 export const WidgetFootprintSchema = {
@@ -4721,7 +4727,7 @@ export const WidgetFootprintSchema = {
         },
         type: {
             type: 'string',
-            enum: ['stat', 'gauge', 'chart', 'markdown', 'agenda', 'notification', 'bar', 'icon', 'forecast', 'clock', 'media', 'player', 'embed', 'button', 'buttons', 'switch', 'slider', 'input', 'dropdown', 'color'],
+            enum: ['stat', 'gauge', 'chart', 'markdown', 'agenda', 'notification', 'bar', 'icon', 'forecast', 'clock', 'media', 'player', 'embed', 'button', 'buttons', 'switch', 'slider', 'input', 'dropdown', 'color', 'counter'],
             title: 'Type'
         }
     },

frontend/src/client/types.gen.ts

@@ -1522,10 +1522,16 @@ export type WebPushKey = {
  * A slider may also show what it is setting: ``reading`` binds
  * ``{message, dtype, label}`` — a room's temperature beside its setpoint —
  * held to the same numbers its target is.
+ *
+ * A counter publishes one number to its target, of which its ``counters``
+ * are the digits: up to three ``{label, step, size, min, max}``, coarsest
+ * first, so hours and minutes publish 07:30 as 450. ``wrap`` says whether it
+ * wraps round at its ends; ``docs/interface/dashboards.md`` has the
+ * arithmetic.
  */
 export type WidgetDef = {
     id: string;
-    type: 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'buttons' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color';
+    type: 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'buttons' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color' | 'counter';
     title?: string;
     layout?: {
         [key: string]: Placement;
@@ -1535,7 +1541,7 @@ export type WidgetDef = {
     };
 };
 
-export type type = 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'buttons' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color';
+export type type = 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'buttons' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color' | 'counter';
 
 /**
  * A widget reduced to the shape it draws: what it is, and where it sits.
@@ -1550,7 +1556,7 @@ export type WidgetFootprint = {
     y?: number;
     w?: number;
     h?: number;
-    type: 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'buttons' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color';
+    type: 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'buttons' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color' | 'counter';
 };
 
 export type WorkerInfo = {

frontend/src/components/Common/DashboardMosaic.tsx

@@ -17,6 +17,7 @@ const INPUT = new Set([
   "input",
   "dropdown",
   "color",
+  "counter",
 ])
 
 const shade = (type: string) =>

frontend/src/components/Dashboard/CounterWidget.tsx

@@ -0,0 +1,85 @@
+import { ChevronDown, ChevronUp } from "lucide-react"
+import { Fragment } from "react"
+
+import { usePublish } from "./publish"
+import { useUi } from "./ui"
+import { countersOf, wrapsOf } from "./ui/core/config"
+import { rangeOf, stepCounter, writtenOf } from "./ui/core/counter"
+import { useRingDraft } from "./ui/core/ring"
+import type { WidgetProps } from "./widgets"
+
+/**
+ * One number set by its digits: hours and minutes, say, published as minutes.
+ *
+ * A column per counter, a press up over its digits and one down under them,
+ * its label beneath. A press moves the value at once, carrying into the
+ * counter beside it, and one publish follows once the presses stop, as a
+ * round face's ring does (`useRingDraft`).
+ */
+export function CounterWidget({ widget, dashboard }: WidgetProps) {
+  const { Button } = useUi()
+  const { target, value, send, pulse, locked } = usePublish(widget, dashboard)
+  const counters = countersOf(widget)
+  const { current, latest, move } = useRingDraft(
+    typeof value === "number" ? value : rangeOf(counters).lo,
+    send,
+  )
+  if (!target) return <p className="text-muted-foreground">Pick a message.</p>
+
+  const written = writtenOf(counters, current)
+  const press = (index: number, by: number) =>
+    move(stepCounter(counters, wrapsOf(widget), latest(), index, by), true)
+  return (
+    <fieldset aria-label={widget.title || target} className="dui-counter">
+      {pulse}
+      {counters.map((counter, index) => {
+        const column = 2 * index + 1
+        const name = counter.label || `Counter ${index + 1}`
+        return (
+          // Two counters may share a label; position is the identity.
+          <Fragment key={`counter-${index}`}>
+            {index > 0 ? (
+              <span
+                aria-hidden
+                className="dui-counter-digits"
+                style={{ gridColumn: column - 1, gridRow: 2 }}
+              >
+                :
+              </span>
+            ) : null}
+            <div style={{ gridColumn: column, gridRow: 1 }}>
+              <Button
+                label={`${name} up`}
+                disabled={locked}
+                onClick={() => press(index, 1)}
+              >
+                <ChevronUp className="size-5" aria-hidden />
+              </Button>
+            </div>
+            <span
+              className="dui-counter-digits"
+              style={{ gridColumn: column, gridRow: 2 }}
+            >
+              {written[index]}
+            </span>
+            <div style={{ gridColumn: column, gridRow: 3 }}>
+              <Button
+                label={`${name} down`}
+                disabled={locked}
+                onClick={() => press(index, -1)}
+              >
+                <ChevronDown className="size-5" aria-hidden />
+              </Button>
+            </div>
+            <span
+              className="text-muted-foreground"
+              style={{ gridColumn: column, gridRow: 4 }}
+            >
+              {counter.label}
+            </span>
+          </Fragment>
+        )
+      })}
+    </fieldset>
+  )
+}

frontend/src/components/Dashboard/RingWidget.tsx

@@ -1,6 +1,6 @@
 import { Lock } from "lucide-react"
 import { type MotionValue, motion, useTransform } from "motion/react"
-import { useEffect, useId, useRef } from "react"
+import { Fragment, useEffect, useId, useRef, useState } from "react"
 
 import type { WidgetDef } from "@/client"
 import { cn } from "@/lib/utils"
@@ -17,15 +17,26 @@ import {
 } from "./ui/core/color"
 import {
   config,
+  countersOf,
   format,
   fractionOf,
   num,
   showTitle,
   text,
+  wrapsOf,
 } from "./ui/core/config"
 import { TESTID } from "./ui/core/contract"
 import { tickIntervals } from "./ui/core/controls"
 import {
+  type Counter,
+  cycleAt,
+  cycleOf,
+  rangeOf,
+  stepCounter,
+  writtenOf,
+} from "./ui/core/counter"
+import {
+  CENTRE_CAPTION,
   CENTRE_LABEL,
   CENTRE_SWATCH,
   CENTRE_VALUE,
@@ -34,11 +45,13 @@ import {
   GAP_RISE,
   GAP_SIZE,
   GAP_WIDTH,
+  RING_DRAG_STEP,
   RING_HANDLE,
   RING_INSET,
   RING_MARK,
   RING_READING,
   RING_STROKE,
+  RING_SWEEP,
   ringArc,
   ringPoint,
   TITLE_RISE,
@@ -76,6 +89,9 @@ type Dial = {
   at: (value: unknown) => number | null
   notch?: (value: unknown, by: number) => unknown
   pick?: (fraction: number, value: unknown) => unknown
+  /** A drag that counts notches rather than picking a place: one per this
+   *  many degrees along the ring, either way. */
+  drag?: number
   /** What it publishes, in the shape the same widget sends from the grid. */
   wire: (value: unknown) => unknown
   /** Written out; empty for a colour, whose handle is the reading. */
@@ -89,9 +105,13 @@ type Dial = {
    *  slider's ticks. */
   stops?: number[]
   hue?: boolean
+  /** Where it stands in a turn rather than along a range, so a move across
+   *  the seam jumps, as a hue does. */
+  wraps?: boolean
 }
 
-function dialOf(widget: WidgetDef, live: unknown): Dial {
+/** `selected` is the counter a counter's ring turns. */
+function dialOf(widget: WidgetDef, live: unknown, selected: number): Dial {
   const cfg = config(widget)
   const unit = cfg.unit ? text(cfg.unit) : undefined
 
@@ -145,6 +165,26 @@ function dialOf(widget: WidgetDef, live: unknown): Dial {
     }
   }
 
+  if (widget.type === "counter") {
+    // The selected counter, stepped with carry; its arc is where it stands
+    // in its turn, as a minute hand stands in the hour.
+    const counters = countersOf(widget)
+    const wrap = wrapsOf(widget)
+    const cycle = cycleOf(counters, selected)
+    const step = counters[selected].step ?? 1
+    return {
+      value: typeof live === "number" ? live : rangeOf(counters).lo,
+      at: (value) => cycleAt(counters, value as number, selected),
+      notch: (value, by) =>
+        stepCounter(counters, wrap, value as number, selected, by),
+      drag: cycle === null ? RING_DRAG_STEP : (RING_SWEEP * step) / cycle,
+      wire: (value) => value,
+      reading: (value) => writtenOf(counters, value as number).join(":"),
+      fill: true,
+      wraps: true,
+    }
+  }
+
   const min = num(cfg.min, 0)
   const max = num(cfg.max, 100)
 
@@ -260,7 +300,7 @@ export function CentreReading({
 /**
  * One widget, drawn along the edge of a round face.
  *
- * A slider, a selector, a colour or a gauge — each is one value along a range,
+ * A slider, a selector, a colour, a gauge or a counter — each is one value,
  * which is the one thing a knob's ring can set and a circle's edge can show.
  * Turned by a drag along it or by the mouse wheel, a notch a step, an option
  * or a hue step; the value moves at once and one publish follows once the
@@ -297,7 +337,16 @@ export function Ring({
   const beside: Series =
     widget.type === "slider" ? ((cfg.reading ?? {}) as Series) : {}
   const read = useBoundValue(beside.message || undefined)
-  const dial = dialOf(widget, widget.type === "gauge" ? bound?.value : value)
+  // The counter the ring turns: the finest until another is pressed, and
+  // again once the face is left.
+  const counters = widget.type === "counter" ? countersOf(widget) : []
+  const [chosen, choose] = useState<number | null>(null)
+  const selected = Math.min(chosen ?? Infinity, counters.length - 1)
+  const dial = dialOf(
+    widget,
+    widget.type === "gauge" ? bound?.value : value,
+    selected,
+  )
   const { current, held, latest, move, commit } = useRingDraft(
     dial.value,
     (next) => send(dial.wire(next)),
@@ -305,9 +354,12 @@ export function Ring({
   const svg = useRef<SVGSVGElement>(null)
   const face = useRef<HTMLDivElement>(null)
   const spin = useRef(0)
+  // Where a counting drag last was, and how far it has gone since its last
+  // notch, in degrees.
+  const dragged = useRef({ angle: 0, by: 0 })
   const turns = Boolean(dial.notch) && !locked
   const at = dial.at(current)
-  const along = useEased(at ?? 0, held, Boolean(dial.hue))
+  const along = useEased(at ?? 0, held, Boolean(dial.hue || dial.wraps))
   // At the minimum the value arc is a zero-length dash whose round caps would
   // still paint a dot, so it is not drawn there.
   const shown = useTransform(along, (fraction) => (fraction > 0 ? 1 : 0))
@@ -338,19 +390,25 @@ export function Ring({
     return () => canvas?.removeEventListener("wheel", listener)
   }, [])
 
-  const aim = (event: React.PointerEvent) => {
+  const aim = (event: React.PointerEvent, start = false) => {
     const box = svg.current?.getBoundingClientRect()
-    if (!box || !dial.pick) return
-    move(
-      dial.pick(
-        fractionAt(
-          event.clientX - (box.left + box.width / 2),
-          event.clientY - (box.top + box.height / 2),
-        ),
-        latest(),
-      ),
-      false,
-    )
+    if (!box) return
+    const dx = event.clientX - (box.left + box.width / 2)
+    const dy = event.clientY - (box.top + box.height / 2)
+    if (dial.drag && dial.notch) {
+      // Counted as a knob's ring counts its detents, the shorter way round
+      // from the last move, so a drag carries on through the gap.
+      const angle = (Math.atan2(dy, dx) * 180) / Math.PI
+      const last = dragged.current
+      last.by = start ? 0 : last.by + ((angle - last.angle + 540) % 360) - 180
+      last.angle = angle
+      const steps = Math.trunc(last.by / dial.drag)
+      if (!steps) return
+      last.by -= steps * dial.drag
+      move(dial.notch(latest(), steps), false)
+      return
+    }
+    if (dial.pick) move(dial.pick(fractionAt(dx, dy), latest()), false)
   }
 
   const title = showTitle(widget) ? widget.title || "" : ""
@@ -495,7 +553,7 @@ export function Ring({
                 return
               }
               event.currentTarget.setPointerCapture(event.pointerId)
-              aim(event)
+              aim(event, true)
             }}
             onPointerMove={(event) => {
               if (event.currentTarget.hasPointerCapture(event.pointerId)) {
@@ -554,7 +612,15 @@ export function Ring({
         </>
       )}
 
-      {dial.hue ? (
+      {widget.type === "counter" ? (
+        <CounterCentre
+          counters={counters}
+          value={current as number}
+          selected={selected}
+          // Nothing to choose between with one, or with a ring that is locked.
+          onSelect={counters.length > 1 && turns ? choose : undefined}
+        />
+      ) : dial.hue ? (
         <div className="pointer-events-none absolute inset-0 flex items-center justify-center">
           <span
             data-testid="face-centre"
@@ -577,6 +643,71 @@ export function Ring({
   )
 }
 
+/**
+ * A counter's digits, written as large as a reading, each over its label.
+ *
+ * The digits are sized as one reading (`fitSize` of all of them, colons and
+ * all), and the pair is centred on the face as the clock's time and date are.
+ * A press on a counter's digits picks it for the ring, and the one it turns
+ * is drawn in the primary colour.
+ */
+function CounterCentre({
+  counters,
+  value,
+  selected,
+  onSelect,
+}: {
+  counters: Counter[]
+  value: number
+  selected: number
+  onSelect?: (index: number) => void
+}) {
+  const written = writtenOf(counters, value)
+  const fontSize = fitSize(written.join(":"), CENTRE_VALUE)
+  return (
+    <div className="pointer-events-none absolute inset-0 flex items-center justify-center">
+      <div
+        data-testid="face-centre"
+        className="flex items-start leading-none tabular-nums"
+      >
+        {counters.map((counter, index) => {
+          const marked = onSelect && index === selected
+          return (
+            // Two counters may share a label; position is the identity.
+            <Fragment key={`counter-${index}`}>
+              {index > 0 ? (
+                <span aria-hidden style={{ fontSize }}>
+                  :
+                </span>
+              ) : null}
+              <button
+                type="button"
+                data-testid={`counter-${index}`}
+                aria-pressed={onSelect ? index === selected : undefined}
+                disabled={!onSelect}
+                className={cn(
+                  "flex flex-col items-center gap-1",
+                  onSelect && "pointer-events-auto",
+                  marked && "text-primary",
+                )}
+                onClick={() => onSelect?.(index)}
+              >
+                <span style={{ fontSize }}>{written[index]}</span>
+                <span
+                  className={cn(!marked && "text-muted-foreground")}
+                  style={{ fontSize: CENTRE_CAPTION, lineHeight: 1.35 }}
+                >
+                  {counter.label}
+                </span>
+              </button>
+            </Fragment>
+          )
+        })}
+      </div>
+    </div>
+  )
+}
+
 /**
  * The ring's dots: its stops, and what a slider reads beside its value.
  *

frontend/src/components/Dashboard/RoundFace.tsx

@@ -87,6 +87,7 @@ export const RING_TYPES = new Set<WidgetKind>([
   "dropdown",
   "color",
   "gauge",
+  "counter",
 ])
 
 /**

frontend/src/components/Dashboard/panels.tsx

@@ -71,10 +71,13 @@ import {
 import {
   type BarRow,
   type ButtonEntry,
+  countersOf,
   MAX_ROWS,
   rowsOf,
   showTitle,
+  wrapsOf,
 } from "./ui/core/config"
+import { type Counter, MAX_COUNTERS } from "./ui/core/counter"
 import { parsePalette, roleLabel } from "./ui/core/theme"
 import {
   acceptsDtype,
@@ -546,6 +549,15 @@ export function WidgetPanel({
   const written = (cfg.buttons ?? []) as ButtonEntry[]
   const buttons: ButtonEntry[] = written.length ? written : [{}]
   const setButtons = (next: ButtonEntry[]) => set({ buttons: next })
+  // A counter's counters, coarsest first. Position is the identity, and the
+  // meaning: the first carries the range, the others a size.
+  const counters = countersOf(widget)
+  const setCounter = (index: number, changes: Partial<Counter>) =>
+    set({
+      counters: counters.map((other, at) =>
+        at === index ? { ...other, ...changes } : other,
+      ),
+    })
   const querying = cfg.source === "query"
   const pinnedRuns = cfg.source === "runs"
   // What this chart would refresh at with nothing configured. The viewer can
@@ -1325,6 +1337,131 @@ export function WidgetPanel({
           </div>
         ) : null}
 
+        {widget.type === "counter" ? (
+          <div className="grid gap-2">
+            <span className={PANEL_SECTION}>Counters</span>
+            <InfoTip label="Counters">
+              Coarsest first, each a label and a step, then the range on the
+              first and a size on the others: how many of it make one of the
+              counter before it. Together they are one number in the last
+              one's unit, so hours and minutes send 07:30 as 450.
+            </InfoTip>
+            {counters.map((counter, index) => (
+              <div
+                // Position is the only identity a counter row has.
+                key={`counter-${index}`}
+                className="flex items-end gap-1.5"
+              >
+                <Input
+                  className="min-w-0 flex-1"
+                  value={counter.label ?? ""}
+                  placeholder="Label"
+                  aria-label="Counter label"
+                  onChange={(event) =>
+                    setCounter(index, { label: event.target.value })
+                  }
+                />
+                <Input
+                  type="number"
+                  className="w-16"
+                  min={1}
+                  placeholder="Step"
+                  aria-label="Counter step"
+                  value={str(counter.step)}
+                  onChange={(event) =>
+                    setCounter(index, {
+                      step: numberOrNone(event.target.value),
+                    })
+                  }
+                />
+                {index === 0 ? (
+                  <>
+                    <Input
+                      type="number"
+                      className="w-16"
+                      placeholder="Min"
+                      aria-label="Counter minimum"
+                      value={str(counter.min)}
+                      onChange={(event) =>
+                        setCounter(index, {
+                          min: numberOrNone(event.target.value),
+                        })
+                      }
+                    />
+                    <Input
+                      type="number"
+                      className="w-16"
+                      placeholder="Max"
+                      aria-label="Counter maximum"
+                      value={str(counter.max)}
+                      onChange={(event) =>
+                        setCounter(index, {
+                          max: numberOrNone(event.target.value),
+                        })
+                      }
+                    />
+                  </>
+                ) : (
+                  <Input
+                    type="number"
+                    className="w-16"
+                    min={1}
+                    placeholder="Size"
+                    aria-label="Counter size"
+                    value={str(counter.size)}
+                    onChange={(event) =>
+                      setCounter(index, {
+                        size: numberOrNone(event.target.value),
+                      })
+                    }
+                  />
+                )}
+                {counters.length > 1 ? (
+                  <Button
+                    variant="ghost"
+                    size="icon-sm"
+                    className="text-muted-foreground"
+                    aria-label="Remove counter"
+                    onClick={() =>
+                      set({
+                        counters: counters.filter((_, at) => at !== index),
+                      })
+                    }
+                  >
+                    <X />
+                  </Button>
+                ) : null}
+              </div>
+            ))}
+            {counters.length < MAX_COUNTERS ? (
+              <Button
+                variant="outline"
+                size="sm"
+                className="h-8 justify-self-start"
+                // A finer one, after the last.
+                onClick={() =>
+                  set({ counters: [...counters, { step: 1, size: 60 }] })
+                }
+                data-testid="add-counter"
+              >
+                <Plus />
+                Add counter
+              </Button>
+            ) : null}
+            <div className="flex items-center justify-between gap-2 text-sm">
+              <FieldLabel help="Past the last value it starts again from the first, as 23:55 goes on to 00:00. Off, it stops at either end. Without a maximum it only stops at the minimum.">
+                Wrap round
+              </FieldLabel>
+              <Switch
+                checked={wrapsOf(widget)}
+                aria-label="Wrap round"
+                data-testid="counter-wrap"
+                onCheckedChange={(wrap) => set({ wrap })}
+              />
+            </div>
+          </div>
+        ) : null}
+
         {widget.type === "icon" ? (
           <div className="grid gap-2">
             <span className={PANEL_SECTION}>Mapping</span>

frontend/src/components/Dashboard/ui/core/config.ts

@@ -7,6 +7,7 @@
  * ends the duplication — nothing in `ui/` may import a widget.
  */
 import type { WidgetDef } from "@/client"
+import { type Counter, DEFAULT_COUNTERS, MAX_COUNTERS } from "./counter"
 
 export const config = (widget: WidgetDef): Record<string, unknown> =>
   (widget.config ?? {}) as Record<string, unknown>
@@ -149,3 +150,17 @@ export function rowsOf(widget: WidgetDef): BarRow[] {
       : []
   return [...outer, ...inner].slice(0, MAX_ROWS)
 }
+
+/** A counter widget's counters, coarsest first: a time of day when it stores
+ *  none (`DEFAULT_COUNTERS`). */
+export function countersOf(widget: WidgetDef): Counter[] {
+  const stored = config(widget).counters
+  return Array.isArray(stored) && stored.length
+    ? (stored as Counter[]).slice(0, MAX_COUNTERS)
+    : DEFAULT_COUNTERS
+}
+
+/** Whether a counter wraps round at its ends rather than stopping; absent is
+ *  yes, as a time of day does. */
+export const wrapsOf = (widget: WidgetDef): boolean =>
+  config(widget).wrap !== false

frontend/src/components/Dashboard/ui/core/core.css

@@ -185,6 +185,22 @@
   height: auto;
 }
 
+/* A counter: a column per counter, its press up, its digits, its press down
+   and its label, with a colon between two columns' digits. */
+.dui-counter {
+  display: grid;
+  justify-content: center;
+  justify-items: center;
+  align-items: center;
+  gap: 0.25rem 0.5rem;
+}
+
+.dui-counter-digits {
+  font-size: clamp(1.25rem, min(22cqh, 12cqw), 4rem);
+  line-height: 1;
+  font-variant-numeric: tabular-nums;
+}
+
 /* A chart is mostly plot; its legend is the hover readout and goes first. */
 @container (max-height: 150px) {
   .dui-chart .u-legend {

frontend/src/components/Dashboard/ui/core/counter.check.ts

@@ -0,0 +1,83 @@
+/**
+ * The counter's arithmetic, checked: the edges the firmware port must agree on.
+ *
+ *     cd frontend && bun run src/components/Dashboard/ui/core/counter.check.ts
+ */
+import assert from "node:assert/strict"
+import {
+  type Counter,
+  cycleAt,
+  DEFAULT_COUNTERS,
+  digitsOf,
+  rangeOf,
+  stepCounter,
+  weightsOf,
+  writtenOf,
+} from "./counter"
+
+const time = DEFAULT_COUNTERS
+const HOUR = 0
+const MIN = 1
+const at = (h: number, m: number) => h * 60 + m
+
+// Digits and how they are written.
+assert.deepEqual(weightsOf(time), [60, 1])
+assert.deepEqual(digitsOf(time, at(7, 30)), [7, 30])
+assert.deepEqual(writtenOf(time, at(7, 5)), ["07", "05"])
+
+// Carry and borrow.
+assert.equal(stepCounter(time, true, at(7, 55), MIN, 1), at(8, 0))
+assert.equal(stepCounter(time, true, at(8, 0), MIN, -1), at(7, 55))
+assert.equal(stepCounter(time, true, at(7, 30), HOUR, 1), at(8, 30))
+
+// The top is the last value the finest step reaches: 23:55.
+assert.equal(rangeOf(time).top, at(23, 55))
+
+// Wrap: round the day either way.
+assert.equal(stepCounter(time, true, at(23, 55), MIN, 1), 0)
+assert.equal(stepCounter(time, true, 0, HOUR, -1), at(23, 0))
+assert.equal(stepCounter(time, true, 0, MIN, -1), at(23, 55))
+
+// Stop: held at either end, as a slider is.
+assert.equal(stepCounter(time, false, at(23, 55), MIN, 1), at(23, 55))
+assert.equal(stepCounter(time, false, at(23, 30), HOUR, 1), at(23, 55))
+assert.equal(stepCounter(time, false, at(0, 30), HOUR, -1), 0)
+
+// One counter, step 5 to 100: the top is 100 itself, padded to max's width.
+const single: Counter[] = [{ step: 5, max: 100 }]
+assert.equal(rangeOf(single).top, 100)
+assert.equal(stepCounter(single, false, 100, 0, 1), 100)
+assert.equal(stepCounter(single, true, 100, 0, 1), 4)
+assert.deepEqual(writtenOf(single, 5), ["005"])
+
+// No max: no top, nothing to wrap at, still held at min.
+const open: Counter[] = [{ step: 1 }, { step: 15, size: 60 }]
+assert.equal(stepCounter(open, true, at(99, 45), 1, 1), at(100, 0))
+assert.equal(stepCounter(open, true, 0, 1, -1), 0)
+assert.deepEqual(writtenOf(open, at(100, 0)), ["100", "00"])
+assert.equal(cycleAt(open, 0, 0), null)
+
+// Three counters: hours, minutes, seconds.
+const clock: Counter[] = [
+  { step: 1, max: 23 },
+  { step: 1, size: 60 },
+  { step: 10, size: 60 },
+]
+assert.deepEqual(weightsOf(clock), [3600, 60, 1])
+assert.equal(stepCounter(clock, true, 3599, 2, 1), 3609)
+assert.equal(rangeOf(clock).top, 86_390)
+
+// Below zero the digits still add up: floor, and a remainder never negative.
+const signed: Counter[] = [
+  { step: 1, min: -5, max: 5 },
+  { step: 5, size: 60 },
+]
+assert.deepEqual(digitsOf(signed, -5), [-1, 55])
+assert.deepEqual(writtenOf(signed, -5), ["-1", "55"])
+assert.equal(stepCounter(signed, true, at(5, 55), 1, 1), -300)
+
+// The ring's arc: the finest like a minute hand, the coarsest across its range.
+assert.equal(cycleAt(time, at(7, 30), MIN), 0.5)
+assert.equal(cycleAt(time, at(6, 0), HOUR), 0.25)
+
+console.log("counter: ok")

frontend/src/components/Dashboard/ui/core/counter.ts

@@ -0,0 +1,128 @@
+/**
+ * A counter widget's arithmetic: one to three counters that are the digits of
+ * one integer, counted in the unit of the finest. Hours and minutes at 07:30
+ * are 450, and 07:55 stepped five minutes on is 08:00.
+ *
+ * Pure and on its own because the openpanel firmware ports it line for line:
+ * a knob and a browser that disagreed on an edge would set the same face to
+ * two different times. `app/docs/interface/dashboards.md` states the same
+ * formulas.
+ */
+
+/** One counter, as the document stores it. Counters are ordered coarsest
+ *  first. */
+export type Counter = {
+  label?: string
+  /** One press or notch, in this counter's own unit. */
+  step?: number
+  /** How many of it make one of the next coarser counter: 60 minutes. Every
+   *  counter but the coarsest has one. */
+  size?: number
+  /** The range, on the coarsest only and in its own unit. No `max` is no
+   *  upper bound. */
+  min?: number
+  max?: number
+}
+
+/** What a counter widget is until it says otherwise: a time of day. */
+export const DEFAULT_COUNTERS: Counter[] = [
+  { label: "h", step: 1, min: 0, max: 23 },
+  { label: "min", step: 5, size: 60 },
+]
+
+/** How many counters one widget links. Mirrored server-side as `COUNTERS`
+ *  (`app/flow/dashboards.py`). */
+export const MAX_COUNTERS = 3
+
+/** The remainder that is never negative, as a clock's is. */
+const mod = (a: number, b: number) => ((a % b) + b) % b
+
+/** What one unit of each counter is worth in the finest's: the finest 1, each
+ *  coarser one the next finer one's weight times that one's size. */
+export function weightsOf(counters: Counter[]): number[] {
+  const weights = counters.map(() => 1)
+  for (let i = counters.length - 2; i >= 0; i--) {
+    weights[i] = weights[i + 1] * (counters[i + 1].size ?? 1)
+  }
+  return weights
+}
+
+/** Each counter's digit of `value`: floor(value / weight) mod size, and the
+ *  coarsest, which has no size, floor(value / weight). */
+export function digitsOf(counters: Counter[], value: number): number[] {
+  const weights = weightsOf(counters)
+  return counters.map((counter, i) => {
+    const digit = Math.floor(value / weights[i])
+    return i === 0 ? digit : mod(digit, counter.size ?? 1)
+  })
+}
+
+/**
+ * The value's range: `lo`, the highest value the finest step reaches from it
+ * (`top`), and the `period` a wrap counts in. Without a `max` there is no top
+ * and nothing to wrap at.
+ */
+export function rangeOf(counters: Counter[]) {
+  const coarsest = counters[0]
+  const weight = weightsOf(counters)[0]
+  const min = coarsest.min ?? 0
+  const lo = min * weight
+  if (coarsest.max == null) return { lo, top: Infinity, period: null }
+  const period = (coarsest.max - min + 1) * weight
+  const fine = counters[counters.length - 1].step ?? 1
+  return { lo, top: lo + Math.floor((period - 1) / fine) * fine, period }
+}
+
+/**
+ * `value` with counter `index` stepped `by` steps, carrying into and borrowing
+ * from the others. At the ends it wraps round the period, or stops at `lo` and
+ * `top`; without a `max` it only stops at `lo`.
+ */
+export function stepCounter(
+  counters: Counter[],
+  wrap: boolean,
+  value: number,
+  index: number,
+  by: number,
+): number {
+  const next =
+    value + by * (counters[index].step ?? 1) * weightsOf(counters)[index]
+  const { lo, top, period } = rangeOf(counters)
+  if (wrap && period !== null) return lo + mod(next - lo, period)
+  return Math.min(top, Math.max(lo, next))
+}
+
+/**
+ * Every counter's digit of `value` as written: zero-padded to the width of
+ * size − 1 (05), the coarsest to the width of its `max` when it has one (07).
+ */
+export function writtenOf(counters: Counter[], value: number): string[] {
+  return digitsOf(counters, value).map((digit, i) => {
+    const widest = i > 0 ? (counters[i].size ?? 1) - 1 : counters[0].max
+    const width = widest == null ? 0 : String(widest).length
+    const padded = String(Math.abs(digit)).padStart(width, "0")
+    return digit < 0 ? `-${padded}` : padded
+  })
+}
+
+/** How many of counter `index` make one turn of it: its size, or the
+ *  coarsest's range. Null for a coarsest without `max`, which has none. */
+export function cycleOf(counters: Counter[], index: number): number | null {
+  if (index > 0) return counters[index].size ?? 1
+  const { min = 0, max } = counters[0]
+  return max == null ? null : max - min + 1
+}
+
+/** Where counter `index` stands in its turn, 0..1: digit / size, as a minute
+ *  hand stands, and the coarsest (digit − min) / (max − min + 1). */
+export function cycleAt(
+  counters: Counter[],
+  value: number,
+  index: number,
+): number | null {
+  const cycle = cycleOf(counters, index)
+  if (cycle === null) return null
+  const from = index > 0 ? 0 : (counters[0].min ?? 0)
+  const at = (digitsOf(counters, value)[index] - from) / cycle
+  return Math.min(1, Math.max(0, at))
+}

frontend/src/components/Dashboard/ui/core/ring.ts

@@ -31,6 +31,10 @@ export const RING_MARK = 6
 export const RING_READING = 12
 /** How long the ring waits after the last notch before it publishes. */
 export const RING_SETTLE_MS = 300
+/** How far a drag along the ring turns a counter that has no arc, a step at
+ *  a time; one with an arc takes a step per step's share of the sweep, so the
+ *  arc stays under the finger. */
+export const RING_DRAG_STEP = 15
 /** The gap's line — a slider's title and value, when what it reads is in
  *  the middle — centred this far above the bottom of the face, at this size,
  *  and at most this wide: clear of the ring's end caps at any size. */
@@ -56,6 +60,8 @@ export const CENTRE_VALUE = 72
 export const CENTRE_LABEL = 36
 export const CENTRE_SWATCH = 96
 export const CENTRE_FLOOR = 24
+/** A line under a centre reading: a counter's labels. */
+export const CENTRE_CAPTION = 17
 
 /** A switch's or a button's disc, as a diameter. */
 export const PRESS = 128

frontend/src/components/Dashboard/widgets.tsx

@@ -8,6 +8,7 @@ import { BarWidget } from "./BarWidget"
 import { ChartWidget } from "./ChartWidget"
 import { ClockWidget } from "./ClockWidget"
 import { ColorWidget } from "./ColorWidget"
+import { CounterWidget } from "./CounterWidget"
 import { useBoundValue } from "./dataContext"
 // The grid's own rules live beside the components that use them; CSS is
 // chunked per entry, so the sheet is pulled in wherever a widget is drawn.
@@ -22,6 +23,7 @@ import { COLOR_DTYPES, colorFormatOf } from "./ui/core/color"
 import {
   buttonsOf,
   config,
+  countersOf,
   decimalsOf,
   num,
   rowsOf,
@@ -37,6 +39,7 @@ export const INPUT_WIDGETS = new Set([
   "input",
   "dropdown",
   "color",
+  "counter",
 ])
 
 export type WidgetKind = WidgetDef["type"]
@@ -55,6 +58,8 @@ export const WIDGET_DTYPES: Partial<Record<WidgetKind, string[]>> = {
   // answer and a `record` request instead, checked in `widgetIssue`.
   chart: ["float", "int"],
   slider: ["float", "int"],
+  // One number, the digits of which its counters are.
+  counter: ["float", "int"],
   switch: ["bool"],
   agenda: ["list"],
   notification: ["record"],
@@ -102,6 +107,7 @@ export const WIDGET_LABELS: Record<WidgetKind, string> = {
   input: "Input",
   dropdown: "Selector",
   color: "Colour",
+  counter: "Counter",
 }
 
 /** One line per type for the add palette, which searches these too. */
@@ -126,6 +132,7 @@ export const WIDGET_DESCRIPTIONS: Record<WidgetKind, string> = {
   input: "Sends what is typed",
   dropdown: "Picks one of a list of options",
   color: "Picks a colour or brightness",
+  counter: "Sets a number by its digits, such as a time",
 }
 
 /** Default footprint per type, in grid units. */
@@ -150,6 +157,7 @@ export const WIDGET_SIZES: Record<WidgetKind, { w: number; h: number }> = {
   input: { w: 4, h: 2 },
   dropdown: { w: 4, h: 2 },
   color: { w: 4, h: 4 },
+  counter: { w: 3, h: 3 },
 }
 
 /** One line of a chart, as the document stores it. */
@@ -269,6 +277,21 @@ export function widgetIssue(widget: WidgetDef): string | null {
   if (widget.type === "icon" && !(cfg.rules as unknown[] | undefined)?.length) {
     return "This icon has nothing mapped yet."
   }
+  if (widget.type === "counter") {
+    const counters = countersOf(widget)
+    const name = (index: number) =>
+      counters[index].label || `Counter ${index + 1}`
+    // A size is what carries into the counter before it; without one there
+    // is nothing to carry at.
+    const unsized = counters.findIndex(
+      (counter, index) => index > 0 && !(Number(counter.size) >= 1),
+    )
+    if (unsized > 0) return `${name(unsized)} needs a size.`
+    const stalled = counters.findIndex(
+      (counter) => Number(counter.step ?? 1) < 1,
+    )
+    if (stalled >= 0) return `${name(stalled)} needs a step of 1 or more.`
+  }
   return null
 }
 
@@ -869,6 +892,7 @@ const RENDERERS: Partial<
   input: InputWidget,
   dropdown: DropdownWidget,
   color: ColorWidget,
+  counter: CounterWidget,
 }
 
 function WidgetBodyComponent({ widget, dashboard }: WidgetProps) {