So I bought this cheap one on Amazon, it powers itself with a CR2032 battery, very common one and cheap to replace. I wanted something for checking RPM more accurately than the vague needle on my Honda tachometer, especially at idle. I could also use it to check other small engines that don’t have tachs like the snowblower, generator, etc.
The Amazon tach mounts with Velcro, it’s self powered, only need to wrap the induction wire around a spark plug wire, no other connections. I set it for a 4 cylinder 4 stroke, attached the wire and started the outboard. I let it warm up in a barrel, then set idle on Honda tach at 1000, checked Amazon tach, then set idle at 2000, checked Amazon tach. It both cases it was very accurate compared to Honda, bouncing say 1080 to 1020, did similar at 2000, 1980-2020 so it seemed accurate and consistent no matter the rpm.
I let it idle and it’s at about 730. All numbers at idle. I am happy with my purchase.
You can set the refresh rate a bit slower, that may have stabilized the about 40 rpm bounce but I didn’t bother doing that.
The induction wire that came with the device is only about 3 ft long, which worked fine for me as I don’t plan to permanently mount it, just use it as a tool for checking/setting rpm on gas engines. This one was self powered, easy to hook up, battery was replaceable, and very cheap. I paid under US$25 including shipping.
https://www.amazon.ca/Runleader-RL-HM032R-tachometer
