Dr. Steve Rapp, 2005
Rules for Writing SI Units
3. Units symbols are unaltered in the plural.
4. Plurals of the unit names are made using
the rules of English grammar.
5. Do not use self-styled abbreviations (i.e.,
sec for second).
6. A space is placed between the symbol and
7. There is no period following the symbol
except if it occurs at the end of a sentence.