RioRand 0.56" Digital Motor LED Tachometer RPM Speed Measure Gauge Meter Tester 60-9999 (Red)

Don't waste your money....bought one didn't work, bought another it didn't. work either, said forget it went a different route

I think you guys are hooking this thing up wrong? I had no problems. I used "HONEYWELL S&C - 103SR13A-1 - HALL EFFECT MAGNETIC SENSOR" (also Amazon prime) on 12vdc. Hook like colors together. Power both reds +, Both blacks -. Tie both greens together and dont connect them to anything else. It reads lower than advertised, I was able to read down to 20 rpm. It moves the decimal point as needed. This isn't for your car engine if that's what you're looking for. You need to attach a dedicated sensor like the one I mentioned above in a way that gives one pulse per revolution.

When I got it, It's show just only 3 digits from 4 digits.