Faria Beede Instruments Chesapeake Black SS 4" Tachometer - 7000 RPM Gas - All Outboards. 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 Black SS 4" Tachometer: Manufacturer: Faria Beede Instruments Color: Black Features of Faria Beede Instruments Chesapeake Black SS 4" Tachometer Perimeter-lighted black dial Stylish blue and white graphics Polished Stainless Steel bezel Domed glass lens Package Contents: Faria Beede Instruments Chesapeake Black SS 4" Tachometer Faria Beede Instruments 33718: Chesapeake Black SS 4" Tachometer - 7000 RPM Gas - All Outboards