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# Unit

An abstract class representing a unit of measure.

```
class Unit
```

## Overview

Each instance of an [`Unit`](/documentation/Foundation/Unit) subclass consists of a [`symbol`](/documentation/Foundation/Unit/symbol), which can be used to create string representations of [`NSMeasurement`](/documentation/Foundation/NSMeasurement) objects with the [`MeasurementFormatter`](/documentation/Foundation/MeasurementFormatter) class.

The [`Dimension`](/documentation/Foundation/Dimension) subclass is an abstract class that represents a dimensional unit, which can be converted into different units of the same type. The Foundation framework provides several concrete [`Dimension`](/documentation/Foundation/Dimension) subclasses to represent the most common physical quantities, including mass, length, duration, and speed.

### Subclassing Notes

[`Unit`](/documentation/Foundation/Unit) is intended for subclassing. For dimensional units, you should use one of the Apple provided [`Dimension`](/documentation/Foundation/Dimension) subclasses listed in Table 1 of [`Dimension`](/documentation/Foundation/Dimension), or create a custom subclass of [`Dimension`](/documentation/Foundation/Dimension). You can create a direct subclass of [`Unit`](/documentation/Foundation/Unit) to represent a custom dimensionless unit, such as a count, score, or ratio.

## Topics

### Accessing Properties

[`symbol`](/documentation/Foundation/Unit/symbol)

The symbolic representation of the unit.

### Creating Units

[`-  initWithSymbol:`](/documentation/Foundation/Unit/init(symbol:))

Initializes a new unit with the specified symbol.

## Relationships

### Inherited By

[`EnergyKit`](/documentation/Foundation/UnitEnergy/EnergyKit)

[`Dimension`](/documentation/Foundation/Dimension)

### Conforms To

[`NSCopying`](/documentation/Foundation/NSCopying)

[`Sendable`](/documentation/Swift/Sendable)

[`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible)

[`NSCoding`](/documentation/Foundation/NSCoding)

[`CVarArg`](/documentation/Swift/CVarArg)

[`Hashable`](/documentation/Swift/Hashable)

[`Equatable`](/documentation/Swift/Equatable)

[`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol)

[`NSSecureCoding`](/documentation/Foundation/NSSecureCoding)

[`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible)

[`SendableMetatype`](/documentation/Swift/SendableMetatype)

### Inherits From

[`NSObject-swift.class`](/documentation/ObjectiveC/NSObject-swift.class)

---

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