Faria Beede Instruments Tachometer w/Hourmeter 4000 RPM Diesel Mech. Takeoff & Var. Ratio Alt 4". Takeoff & Var. Ratio AltHole Size: 4"Perimeter-lighted black dial with bold white graphics black aluminum SAE style bezel contoured white pointer and flat glass lens.Electronic tachometers work by counting pulses generated by the ingition system alternator tach signal generator or magnetic pickup sender. The tach is hooked up to +12vDC Ground and one of hte signal sources listed above.By selecting the right tach and setting the switch on the back to the correct postion you let the tachometer know how many pulses are sent per each engine revolution. Specifications for Faria Beede Instruments 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech. Takeoff & Var. Ratio Alt: Manufacturer: Faria Beede Instruments Color: Black Features of Faria Beede Instruments 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 Anti-scratch glass lens Package Contents: Faria Beede Instruments 4" Tachometer w/Hourmeter 4000 RPM Diesel Mech. Takeoff & Var. Ratio Alt Faria Beede Instruments 33834: Tachometer w/Hourmeter 4000 RPM Diesel Mech. Takeoff & Var. Ratio Alt 4"