Inaccurate Tach

[KyleTownsend]

Bought one of those little "prop tach" optical tachs from Sporty's. It just came in a couple of days ago.

Been out flying around some, and find that my factory tachs are off by about 100 RPM (reading too high).

Since they are overstating RPM it's no big deal. I've just been flying around at lower power settings than I thought.

Would be a different story if they were reading 100 too low. That's definitely enough to make a pretty big difference on the power charts. Could have been really bad for the engines.

Wonder if anyone else has run into this, and whether or not you can calibrate the factory tachs?