Unit prefix support seems spotty. For example, 1,'m,'mm,convert correctly gives 1000 'mm', but 1,'W,'mW,convert results in an unknown unit. kW is defined as a separate unit for some reason. Another strange result is 1,'m,'fm',convert, which returns 1 'fm'. I would expect all SI prefixes
to be supported for all SI units, and maybe even the binary ones
. The prefixes don't appear to be part of the Units folder, so adding extra doesn't seem trivial.