We recommend adhering to the CF convention's guidance on the use of the units attribute with the following clarifications:
- Unitless (dimensionless in the physical sense) property of the data in a variable is indicated by the lack of a units attribute, unless:
- appropriate physical units do exist;
- use of dimensionless units identifiers is common practice in the target user community.
- Values of the units attribute should be supported by the UDUNITS-2 library.
- A variable used in any context other than data storage should never have the units attribute.