Faria Beede Instruments Tachometer w/Digital Hourmeter 6000 RPM Gas Inboard Chesapeake White w/Stainless Steel Bezel 5". Electronic tachometers work by counting pulses generated by the ignition system alternator tach signal generator or magnetic pickup sender. These counts pulse tachometers are 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 Faria Beede Instruments tachometers are very accurate more durable and easier to read than mechanical tachometers. Choosing the right tach and setting the switch on the back correctly is very important. Getting the right tach and setting the switch on the back correctly is very important. You let the tachometer know how many pulses are sent per each engine revolution. Having the switch on the back allow you to let the tachometer know how many counts per each engine revolution. The more signal sources an electronic tachometer is hooked up to the more accurate the tachometer will be. Specifications for Faria Beede Instruments 5" Tachometer w/Digital Hourmeter 6000 RPM Gas Inboard Chesapeake White w/Stainless Steel Bezel: Manufacturer: Faria Beede Instruments Color: Silver Features of Faria Beede Instruments 5" Tachometer w/Digital Hourmeter 6000 RPM Gas Inboard Chesapeake White w/Stainless Steel Bezel Wide range of scales Available for gas or diesel engines Multiple signal sources Anti-scratch glass lens Plastic Cases for corrosion resistance and long life Chesapeake White with Stainless Steel Bezel Package Contents: Faria Beede Instruments 5" Tachometer w/Digital Hourmeter 6000 RPM Gas Inboard Chesapeake White w/Stainless Steel Bezel Faria Beede Instruments 33863: Tachometer w/Digital Hourmeter 6000 RPM Gas Inboard Chesapeake White w/Stainless Steel Bezel 5"