---
title: UnitDispersion
framework: foundation
role: symbol
role_heading: Class
path: foundation/unitdispersion
---

# UnitDispersion

A unit of measure for specific quantities of dispersion.

## Declaration

```swift
class UnitDispersion
```

## Overview

Overview You typically use instances of UnitDispersion to represent specific quantities of dispersion using the NSMeasurement class. Dispersion Dispersion describes the amount of a constituent divided by the amount of all other constituents in a mixture. Dispersion is a dimensionless quantity that is commonly expressed in “parts-per” notation, such as “parts per million” (ppm), to describe small relative quantities. The UnitDispersion class defines its baseUnit() as partsPerMillion.  |  |   |  |

## Topics

### Accessing the Base Unit

- [baseUnit()](foundation/dimension/baseunit().md)

### Accessing Predefined Units

- [partsPerMillion](foundation/unitdispersion/partspermillion.md)

## Relationships

### Inherits From

- [Dimension](foundation/dimension.md)

### Conforms To

- [CVarArg](swift/cvararg.md)
- [CustomDebugStringConvertible](swift/customdebugstringconvertible.md)
- [CustomStringConvertible](swift/customstringconvertible.md)
- [Equatable](swift/equatable.md)
- [Hashable](swift/hashable.md)
- [NSCoding](foundation/nscoding.md)
- [NSCopying](foundation/nscopying.md)
- [NSObjectProtocol](objectivec/nsobjectprotocol.md)
- [NSSecureCoding](foundation/nssecurecoding.md)
- [Sendable](swift/sendable.md)
- [SendableMetatype](swift/sendablemetatype.md)

## See Also

### Concentration and Dispersion

- [UnitConcentrationMass](foundation/unitconcentrationmass.md)