The standard name table declares canonical units for each standard name. For some of the dimensionless quantities these can be other than "1" (for example, "sea_surface_salinity" uses "1e-3"). So the question is, for a quantity such as "sea_surface_salinity", if it appears in a CF file without a "units" attribute, should we assume the units are "1" or "1e-3"? I'm not sure, but I'm OK with dealing with this in a separate issue/PR.