Open a 3-3/8 inch dimension and 2-3/4 inch depth hole, put gauge into it and fasten Using stepper motor drive pointer, accurate display of the engine speed, and with the LCD display clear display mileage. It takes about to get signal in the first time, but less than 3 seconds after that. It gets quicker under a clear view of the . Sometimes if signal is missing, pls. reconnect all wires and restart it. Tachometer fit for Car /Truck/ Boat /crude oil Generator Engine /Gasoline Engine Speedometer Less power consumption, longer life, higher precision,quick location confirmation, short start up time Speedometer: 120 Km/h Voltage: 12V/24V Applicable models: Colour:black Material:stainless steel Size:85mm Package Contents: 1 * 120 Km/h Speedmeter 1 * Chinese and English manual 1 * Multi-plug socket Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.