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# units

The units of the characteristic value.

```
var units: String? { get }
```

## Discussion

The [`units`](/documentation/HomeKit/HMCharacteristicMetadata/units) property tells you how to use the corresponding characteristic’s [`value`](/documentation/HomeKit/HMCharacteristic/value) in calculations or how to format it for presentation. For example, you can extend the [`HMCharacteristic`](/documentation/HomeKit/HMCharacteristic) class with a computed property that returns the appropriate symbol to accompany the value in printed output:

```swift
extension HMCharacteristic {
    var symbol: String {
        guard let units = metadata?.units else { return "" }

        switch units {
        case HMCharacteristicMetadataUnitsPercentage:              return "%"
        case HMCharacteristicMetadataUnitsPartsPerMillion:         return "ppm"
        case HMCharacteristicMetadataUnitsCelsius:                 return "°C"
        case HMCharacteristicMetadataUnitsFahrenheit:              return "°F"
        case HMCharacteristicMetadataUnitsSeconds:                 return "s"
        case HMCharacteristicMetadataUnitsLux:                     return "lx"
        case HMCharacteristicMetadataUnitsMicrogramsPerCubicMeter: return "μg/m³"
        case HMCharacteristicMetadataUnitsArcDegree:               return "°"
        default:                                                   return ""
        }
    }
}
```

See [Characteristic Units](/documentation/HomeKit/characteristic-units) for the complete list of possible units.

---

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