Hola, a ver si arrojamos algo de luz.
Si buscamos "Tachometer", en inglés, nos sale esta definición:
"any of various instruments for measuring or indicating velocity or speed, as of a machine, a river, or the blood.
2. an instrument measuring revolutions per minute, as of an engine"
# measuring instrument for indicating speed of rotation
wordnetweb.princeton.edu/perl/webwn
# A tachometer (also called a revolution-counter, rev-counter, or RPM gauge) is an instrument that measures the rotation speed of a shaft or disk, as in a motor or other machine. ...
en.wikipedia.org/wiki/Tachometer
# A device for measuring the revolutions per minute (RPMs) of a revolving shaft, as with the driveshaft of an automobile; A device for measuring or indicating velocity or speed, as of blood, a river, a machine, etc.
en.wiktionary.org/wiki/tachometer
# tachometry - The use of a tachometer
en.wiktionary.org/wiki/tachometry
# TACHOMETER The tachometer is essentially a gauge that can display an engine's revolutions per minute (rpm or revs).
www.autoevolution.com/auto-glossary/t.html
# An instrument that displays revolutions per minute. Submit new or altered description
www.bikez.com/jargon/index.php
# A device used to indicate the speed of the engine in rpm (revolutions or cycler per minut). The tachometer is mounted on the dahboard or the steering wheel. It helps the driver to know the optimum rpm for changing gears on manual transmissions. ...
www.f1technical.net/glossary/t
# A numerical scale on the dial or bezel of a chronograph that can be used in conjunction with the chronograph seconds hand to determine speed over a pre-measured distance, such as a measured mile on a highway.
Es decir, un instrumento para medir o indicar velocidad respecto de una máquina, un río o la sangre; o un instrumento para medir las RPM de un motor (cuentarrevoluciones).
Ahora vamos por TACHYMETER:
"A surveying instrument used for the rapid determination of distances, elevations, and bearings"
Un instrumento para la rápida medida de distancias, elevaciones etc.
PEEERO... Si echamos un ojo a esta página, parece decir que ambas palabras significan lo mismo:
http://www.thewatchery.com/Glossary/Tachometer_/Tachymeter_111.htm
El artículo de la Wikipedia insiste sin embargo en el Término TACHYmeter, para nuestra confusión
http://en.wikipedia.org/wiki/Tachymeter
En fin, que te dejo igual que estabas
En mi opinión TACHOMETER sería cuando la escala mide RPM y TACHYMETER cuando sirve para otros fines... ¿O no?
