Tachometer Calibration = Vital!

Inspired some starting troubles (wanted to make sure the starter was turning the engine fast enough), I bought a TruTach II calibration device. I'd assumed my electrically driven Rotax/Aviasport tach would be accurate, but it does convert to an analog signal to drive the indicator needle. The TruTach showed that it's way off, and in the bad direction - reads low by a lot. An indicated 5,800 rpm would in reality be 6150. As a replacement, I ordered a UMA 19-519-211 guaranteed to +/- 25 rpm. As far as I can determine, there is no TSO'd tachometer for Rotax other than perhaps as part of a full engine monitoring system.