Engine Break-in - How to measure rpms with Helmet Dist?

[Ziggster]

Meter showed up. Tried it at first and nothing. Came with 9 VDC battery, but seemed no good. Swapped in another I had. Tested it on my bench grinder and 5” Makita electric grinder. Works! Bench grinder came in at 3600 rpm and Makita at 8,800. Was about to throw out the battery, then noticed it was covered in a clear plastic film. D’oh! Just came back from my eye exam and she said I had 20/20 which I haven’t had since a teenager, and for reading a 225, whatever that is. Is smaller than I expected, and feels cheap, but works. lol!