Tachometer operates by detecting reflected light rather than a metallic or magnetic target; operating distance 0.25 to 18.0; speed range 0.02 pps to above 6, 000 pps; contains amplifiers and output circuitry, battery charger, light sensor, light source, power supply; 2.625 in. W; 7, 000 in. D; 4.125 in h