Just something to contribute that I learned.

If you want to make sure your tach is operating correctly, set the prop choice to 2 blade and hold it up to a flourescent light. It should read 3600. That's because here in the US, our electricity runs on 60 cycles per second. Multiply that by 60 seconds, and you get 3600.

If it doesn't read 3600, your battery is getting weak or your power company is not up to par.

I may be wrong here, but I believe in England and the rest of Europe, they run on 50 cycles per second, so their tachs would read 3000.

Don't try to tach your engine anywhere near a flourescent light.

Just trying to give back for all that I have learned.