Before revision: 300px|A tachometer that can indicate up to 7000 RPM (left) A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine.
After revision: 300px|A Rpm that can indicate up to 7000 RPM (left) A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine.