This SAE Aerospace Standard (AS) covers tachometer instruments (RPM indicator@ 0-110 percent RPM and 0-120 percent RPM indicators and generator) for remote indication of engine speed. Purpose: This AS establishes the essential minimum safe performance standards for Tachometer Instruments primarily for use on turbine-powered subsonic transport aircraft@ the operation of which may subject the instruments to the environmental conditions specified in Section 3.3.