I have been trying to calibrate engine instruments for my BMA EFIS and have gotten quite an education in the process.  I must be doing something wrong on the calibration table for the RPM channel because the RPM reading is way off the mark.  One problem I'm having is what to use as a reference when checking the accuracy of the RPM readings.  I don't have a prop tach, but that would be one way.  But since I also have an EM-2, it would make sense to use the EM-2 RPM reading as a guide.  But I really don't know how accurate it is.  Has anyone actually verified the rpm readings from the EM-2?  I have no particular reason to question it, but it would be good to know that the EM-2 readings are accurate within some factor.

Mark S.