Review on 2-in-1 Waterproof Motorcycle LED Digital Tachometer & Voltmeter: Metal Odometer Speedometer by John Naidu

Easy installation, voltmeter works properly. I get a tachometer reading, but it seems the calibration is about 1300 rpm too high (it says the engine idle speed is 2000 rpm). I couldn't find an adjustment screw or anything like that on the unit. The description says "Please be patient while calibrating", but how does it work? I'll check and upvote this review if I get an answer to this question as other than that I really like the device.