The Murphy Selectronic MT90-1 is a digital tachometer. Its high accuracy and dependability result from use of a quartz crystal time based and digital, solid state electronics. Tachometer power is supplied by either a Murphy magnetic pickup, mounted at the flywheel ring-gear of an engine, or by a 12, 24, or 32 volt DC battery system. RPM data is supplied by either a Murphy magnetic pickup or by the alternator in your battery charging circuit. The MT90 also has back-lighting for easy readings in low lit areas; this lighting requires a battery power source.