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Type:Number allows a unit after the numeric value to distinguish values (e.g. "30 kg" versus "5 liter/100 km"), but does not know how to convert between them.

To support automatic conversion and multiple unit formats, you can define your own datatype with custom units. These automatically convert values to and from standard representations, so that you are free to use your preferred unit in each article yet still query and compare with property values in other articles.