Faria Beede Instruments 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech Takeoff & Var Ratio Alt Euro. Electronic tachometers work by counting pulses generated by the ignition system alternator tach signal generator or magnetic pickup sender. The tachometer is hooked up to +12VDC Ground and one of the signal sources listed above. By selecting the right tach and setting the switch on the back to the correct position you let the tachometer know how many pulses are sent per each engine revolution. These boating accessories offer rugged reliable construction and are perfect for repairing or maintaining your automobile military vehicle farm equipment ATVs snowmobiles 4000 rpm gas or diesel engines air conditioning units towing refrigerators outboards motorcycles small engines agricultural engines counting vaccines hydraulic hoists etc. For a wide range of scales and signal sources check out the Faria Beede Instruments Euro 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech Takeoff & Var Ratio Alt. Specifications for Faria Beede Instruments Euro 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech Takeoff & Var Ratio Alt: Manufacturer: Faria Beede Instruments Color: Black Features of Faria Beede Instruments Euro 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech Takeoff & Var Ratio Alt Wide range of scales Available for gas or diesel engines Multiple signal sources Rugged Reliable construction 4" - Hole size: 3.375" (85mm) Package Contents: Faria Beede Instruments Euro 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech Takeoff & Var Ratio Alt Faria Beede Instruments 32834: 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech Takeoff & Var Ratio Alt Euro