Needle Gauge

A rotating needle gauge that displays a single numeric value within a range. Supports alert zones, custom styling, and zone-change callbacks.

Playground

info

onZoneChange callbacks work in your local project but not in this interactive playground due to how the editor re-renders components.

Props

Prop	Type	Default	Description
data	RelayDataPoint	—	Required. The value and timestamp — see data
min	number	0	Minimum scale value
max	number	100	Maximum scale value
label	string	—	Label text below the value
unit	string	—	Unit suffix (e.g., "°C")
formatValue	function	—	Custom value formatter — see formatValue
alertZones	AlertZone[]	—	Color zones on the gauge arc — see Alert Zones
showZoneValues	boolean	false	Show boundary values on zone edges
styles	object	—	Custom fonts and background — see Styles
showLastUpdated	boolean	false	Show the timestamp from data.timestamp
formatTimestamp	function	—	Custom timestamp formatter — see formatTimestamp
showLoading	boolean	true	Show skeleton shimmer while data.isLoading is true
onZoneChange	function	—	Called when value enters a new zone — see onZoneChange
onError	function	—	Called on invalid data — see onError

---

data

All components accept a data prop with this shape:

data={{
  value: 65,              // the current reading
  timestamp: Date.now(),  // when the reading was taken (ms)
  isLoading: false,       // optional — shows skeleton shimmer
  error: null,            // optional — triggers onError
}}

Field	Type	Description
value	any	The current reading
timestamp	number | null	When the reading was taken (Unix ms)
isLoading	boolean	(optional) Shows skeleton shimmer when true
error	Error | null	(optional) Triggers the onError callback

When using hooks, this maps directly:

const { value, timestamp, isLoading, error } = useRelayLatest({
  deviceIdent: "sensor_01",
  metric: "temperature",
  timeRange: { start: Date.now() - 86400000, end: Date.now() },
});

<NeedleGauge data={{ value, timestamp, isLoading, error }} />

---

Alert Zones

Color the gauge arc based on value ranges. Each zone needs min, max, color, and an optional label. Zones must not overlap.

Try pasting this into the playground:

alertZones={[
  { min: 0, max: 25, color: "#3b82f6", label: "Cold" },
  { min: 25, max: 50, color: "#22c55e", label: "Normal" },
  { min: 50, max: 75, color: "#f59e0b", label: "Warm" },
  { min: 75, max: 100, color: "#ef4444", label: "Hot" },
]}

The needle color automatically matches the zone it's in. Without alert zones, the gauge renders a single grey arc.

---

Styles

Customize fonts and background via the styles prop. Every font field accepts fontFamily, fontSize, fontWeight, and color.

styles={{
  value: { fontSize: 28, fontWeight: 700, color: "#1e293b" },
  label: { fontSize: 14, color: "#64748b" },
  unit: { fontSize: 12, color: "#94a3b8" },
  minMax: { fontSize: 10, color: "#94a3b8" },
  lastUpdated: { fontSize: 10, color: "#94a3b8" },
  background: { color: "#f8fafc" },
}}

Try adding this to the playground to see the effect:

<NeedleGauge
  data={{ value: 72, timestamp: Date.now() }}
  min={0}
  max={100}
  label="Styled"
  unit="°C"
  styles={{
    value: { fontSize: 32, fontWeight: 800, color: "#7c3aed" },
    label: { fontSize: 16, color: "#a78bfa" },
    background: { color: "#faf5ff" },
  }}
  alertZones={[
    { min: 0, max: 50, color: "#a78bfa" },
    { min: 50, max: 100, color: "#7c3aed" },
  ]}
/>

Style fields reference

Field	Applies to	Properties
value	The large number display	fontFamily, fontSize, fontWeight, color, fontFile
label	The label below the value	fontFamily, fontSize, fontWeight, color, fontFile
unit	The unit suffix	fontFamily, fontSize, fontWeight, color, fontFile
minMax	Min/max labels at arc ends	fontFamily, fontSize, fontWeight, color, fontFile
lastUpdated	The timestamp text	fontFamily, fontSize, fontWeight, color, fontFile
background	The component background	color

Custom Fonts

Use fontFile to load a custom font from a URL. Supports .ttf, .otf, .woff, and .woff2 files. The font is automatically loaded via @font-face — you don't need to add any CSS yourself.

styles={{
  value: {
    fontFile: "/fonts/CustomFont.woff2",
    fontSize: 28,
    fontWeight: 700,
  },
}}

Additional style options:

Field	Type	Default	Description
arcThickness	number	14	Thickness of the gauge arc in pixels
needleThickness	number	2.5	Thickness of the needle in pixels
arcAngle	number	180	Sweep angle of the arc in degrees (30–300)
width	number	—	Fixed width override
height	number	—	Fixed height override

---

formatValue

Override how the value number is displayed. Receives the raw number, returns a string.

formatValue={(v) => v.toFixed(1)}
formatValue={(v) => `~${Math.round(v)}`}
formatValue={(v) => `${v}%`}

---

formatTimestamp

Override how data.timestamp is displayed when showLastUpdated is true.

showLastUpdated={true}
formatTimestamp={(ts) => new Date(ts).toLocaleTimeString()}

---

onZoneChange

Called whenever the value moves from one alert zone to another.

onZoneChange={(transition) => {
  console.log(transition);
  // {
  //   previousZone: { min: 30, max: 70, color: "#22c55e", label: "Normal" },
  //   currentZone:  { min: 70, max: 100, color: "#ef4444", label: "Hot" },
  //   value: 72
  // }
}}

Field	Type	Description
transition.previousZone	AlertZone | null	The zone the value was in
transition.currentZone	AlertZone | null	The zone the value moved to
transition.value	number	The current value

---

onError

Called when the component receives invalid data (NaN, non-finite, non-numeric). The component renders the last valid value and fires this callback.

onError={(error) => {
  console.error(error);
  // {
  //   type: "invalid_value",
  //   message: "NeedleGauge received NaN",
  //   rawValue: NaN,
  //   component: "NeedleGauge"
  // }
}}

Field	Type	Description
error.type	string	"invalid_value", "invalid_data_point", or "invalid_timestamp"
error.message	string	Human-readable error description
error.rawValue	any	The invalid value that was passed
error.component	string	The component name

The component never crashes on bad data — it falls back to the last valid state and notifies you via this callback.

---

With Hooks

import { useRelayLatest, NeedleGauge } from "@relay-x/ui";

function TemperatureGauge() {
  const latest = useRelayLatest({
    deviceIdent: "sensor_01",
    metric: "temperature",
    timeRange: { start: Date.now() - 86400000, end: Date.now() },
  });

  return (
    <NeedleGauge
      data={latest}
      min={0}
      max={100}
      label="Temperature"
      unit="°C"
      showLastUpdated
      alertZones={[
        { min: 0, max: 30, color: "#3b82f6", label: "Cold" },
        { min: 30, max: 70, color: "#22c55e", label: "Normal" },
        { min: 70, max: 100, color: "#ef4444", label: "Hot" },
      ]}
      onZoneChange={(t) => console.log(`Zone: ${t.currentZone?.label}`)}
      onError={(e) => console.error(e.message)}
    />
  );
}