Faria Beede Instruments Chesapeake White SS 4" Tachometer - 4000 RPM Diesel - Magnetic Pick-Up. 375" (85mm)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 the 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.Benefits:Wide range of scales Multiple signal sources Rugged Reliable construction Specifications for Faria Beede Instruments Chesapeake White SS 4" Tachometer: Manufacturer: Faria Beede Instruments Color: White Features of Faria Beede Instruments Chesapeake White SS 4" Tachometer Perimeter-lighted white dial Polished stainless steel bezel Contoured black pointer and domed glass lens Please confirm part will fit before ordering Package Contents: Faria Beede Instruments Chesapeake White SS 4" Tachometer Faria Beede Instruments 33818: Chesapeake White SS 4" Tachometer - 4000 RPM Diesel - Magnetic Pick-Up