A basic introduction to the metric system. Covers: the three classes of SI units & the SI prefixes; units outside the SI; rules & style conventions for printing & using units; rules & style conventions for expressing values of quantities; comments on some quantities & their units; rules & style conventions for spelling unit names; printing & using symbols & numbers in scientific & technical documents; & check list for reviewing manuscripts. Appendix: definitions of SI base units & the radian & Steradian; conversion factors, & comments on the references of the SI for the U.S. Extensive bibliography.