Terry Simpson wrote: >Was 'micron' the only approved name over that period or did it exist in >parallel to 'micrometre'?
Both were valid, as micro was a valid prefix for any SI unit. The micron's symbol (�) had the distinction of being the only Greek letter used as the symbol for both a prefix and a unit. I think adding a prefix to micron would have been even more problematic than with liter (with milliliter [mL] meaning the same as cubic centimeter [cm3]). Imagine millimicrons (m�) competing with nanometers (nm) and micromicrons (��) competing with picometers (pm). Bill Potts, CMS Roseville, CA http://metric1.org [SI Navigator]
