# Units of scale

Tip

All scale units have helper methods `->asUnity()`

, `->add()`

, `->subtract()`

,
`->multiply()`

and `->divide()`

Tip

You can access the list of supported scale units at runtime using `Scale::getSupportedSRIDs()`

or
`Scale::getSupportedSRIDsWithHelp()`

## Unity

```
new Unity(float $number)
Scale::makeUnit(float $number, Scale::EPSG_UNITY)
Scale::makeUnit(float $number, 'urn:ogc:def:uom:EPSG::9201')
```

SI coherent derived unit (standard unit) for dimensionless quantity.

## Coefficient

```
new Coefficient(float $number)
Scale::makeUnit(float $number, Scale::EPSG_COEFFICIENT)
Scale::makeUnit(float $number, 'urn:ogc:def:uom:EPSG::9203')
```

Used when parameters are coefficients. They inherently take the units which depend upon the term to which the coefficient applies.

## Parts per billion

```
new PartsPerBillion(float $number)
Scale::makeUnit(float $number, Scale::EPSG_PARTS_PER_BILLION)
Scale::makeUnit(float $number, 'urn:ogc:def:uom:EPSG::1028')
```

Billion is internationally ambiguous, in different languages being 1E+9 and 1E+12. One billion taken here to be 1E+9.

## Parts per million

```
new PartsPerMillion(float $number)
Scale::makeUnit(float $number, Scale::EPSG_PARTS_PER_MILLION)
Scale::makeUnit(float $number, 'urn:ogc:def:uom:EPSG::9202')
```