Bill,
The context was the measurement of remaining brake pad thickness
in advertising by Midas International in the Washington area, using
the submultiple "micro-millimeter" which is exaggerated in precision
(to a few wavelengths of light for brake pads), and a double-prefix;
objectionable on these two counts.
..................
On Sat, 8 Sep 2001, Bill Hooper wrote: ...
> There is no reason to state that nanometres are "for optical lengths".
Yes there is, in the context of measuring brake pad thickness.
> The nanometre is a perfectly proper unit for ANY very small length...
On this secondary question, my preference is to follow terminology
in the BIPM Brochure, latest edition in print; that *only* the meter
is the "SI unit of length", and that the nanometer is but one of many
acceptable "submultiples" of the meter.
Gene.
