# ConventionalUnit

 ConventionalUnit Plain Definition and Guidance 1 identifier 1 2 name 0..* 3 (choose one) conversionToPreferredUnit roughConversionToPreferredUnit 1

Definition
Conventional units that are neither base units nor defined by direct combination of base units are used in many application domains. For example electronVolt for energy, feet and nautical miles for length. In most cases there is a known, usually linear, conversion to a preferred unit which is either a base unit or derived by direct combination of base units.

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Example showing the conversion for the unit 'foot' to 'meters' using the factor element. In this case the factor element contains a scale factor of 0.305. The scale factor is multiplied by the value of the conventional unit of measure (foot) to obtain the corresponding value for the preferred unit of measure (meter).

```<gml:ConventionalUnit gml:id="ft">
<gml:identifier codeSpace="foot"/>
<gml:conversionToPreferredUnit uom="m">
<gml:factor>0.305</gml:factor>
</gml:conversionToPreferredUnit>
</gml:ConventionalUnit>
```

Example showing the conversion for the unit 'Celsius' to 'Kelvin' using the formula element. The formula element can contain the four elements a,b,c and d, whose values provide the parameters for converting the value of the conventional unit of measure (degrees Celsius) to the corresponding value for the preferred unit of measure (Kelvin). The values of the elements a,b,c and d are used in the formula y = (a + bx) / (c + dx), where x is the value using the current unit, and y is the corresponding value using the preferred unit. Elements a and d are optional. If those values are not provided, then those parameters are considered to be zero. The example below shows the conversion of Celsius to Kelvin so the formula becomes: K = 273.15 + C

```<gml:ConventionalUnit gml:id="degC">
<gml:identifier codeSpace="degree Celsius"/>
<gml:conversionToPreferredUnit uom="K">
<gml:formula>
<gml:a>273.15</gml:a>
<gml:b>1</gml:b>
<gml:c>1</gml:c>
</gml:formula>
</gml:conversionToPreferredUnit>
</gml:ConventionalUnit>
```