There has been remarks about some units not being SI. For example, centimetre, millimetre.
All SI prefix multiples of the coherent SI units are SI units. Reference: IEEE/ASTM SI 10 -2002 2.2 SI prefixes "The term SI units includes the SI base units, the SI derived units, and all units formed from them using the SI prefixes."
At times one sees references to "SI units" meaning only the base units. From this there have been statements that a prefixed unit is not an SI unit. Such statements are in error. It is not reasonable to tell the public to use SI units, (usually said as "Use metric units") and then say that millimetre is not an SI unit. The 1997 edition of SI 10 was not clear on this matter.
The centimetre and millimetre are SI units but they are not SI base units. They are submultiples of SI base units. So also is the gram.
-- Joseph B. Reid 17 Glebe Road West Toronto M5P 1C8 Telephone 416-486-6071
