Since common rail method is mainly used for diesel engines these days, it is getting difficult to measure the rotational speed without a highly sensitive tachometer. The GE-1400 Diesel Engine Tachometer provides higher sensitivity than the previous model, and thus it is easy to get effected and pick up the disturbance signals by nearby cylinders. When you measure rotational speed of the engine for the first time, to prevent the disturbance signals from the other cylinders and obtain exact rotational speed, you should move the trigger level adjustment dial from minimum to maximum watching how the values appear on the display. After that, move it from maximum toward minimum adjusting the level and measure at the place where the value will be stable first.