There's a method/methods here.. http://www.cyclepowermeters.com/powertap-garmin-calibration-check-76-c.asp
Yeah so that's weight off pedal axle method. Plus thats for powertap, not SRM. (know srm in photo)
@skinny started
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There's a method/methods here..
http://www.cyclepowermeters.com/powertap-garmin-calibration-check-76-c.asp