I agree with what has been said by @martinjuckes, @cameronsmith1 and @roy-lowry. I don't think dimensionless units should be used to distinguish between dimensionless quantities, since that's the purpose of standard names, but Roy's preference for explicitly describing the dimensionless ratios makes sense to me. Thus we have these two proposals. We could add both of them to the text:
* CF does not allow `ppmv`, `ppbv` and `pptv`, because the distinction between ratios of volume and other dimensionless ratios should be made by the `standard_name`, not the `units`. * When a dimensionless quantity is a ratio of dimensional quantities, data-writers are encouraged to consider specifying its `units` as a ratio of units, for instance `mg kg-1` or equivalents instead of `ppm` for a mass ratio, and `ul l-1`, `microlitre litre-1` or equivalents for `ppmv`, for clarity, while also providing a `standard_name`. I have phrased the first as a negative requirement (a prohibition), meaning that these units would cause the CF checker to report an error. It could instead be a negative recommendation (a deprecation), so that the CF checker would give a warning. What do you think? On @dopplershift's point, I agree with Roy. I would add that CF relies on udunits only for the definition of possible syntax and legal units, not for the udunits software. I should think that Unidata would be happy to have suggestions for improving the udunits documentation of what is allowed. Unidata have provided a useful resource and CF doesn't have much human resource available, so it is better not to duplicate. The "delegation" to udunits has served us well, I would say. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/260#issuecomment-618915190 This list forwards relevant notifications from Github. It is distinct from [email protected], although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to [email protected].
