These are indeed available. One we use is made by Calculated Industries,
called
ModelCalc. It converts not only m/cm/mm, etc., but also does grade, rise,
radius, and sundry. Available in builders' supply departments. Measure 5
1/2 x 3 inches.
A smaller version, which also does km/ temperatures, etc., was made by Casio,
called Metric Converter MC-34. Mine is very old, and may not still be
available.
Roberta Greenwood