From all accounts it is accurate as long as the dynamic factors match the static calibrations as closely as possible. As soon as those change, i.e. different road surface, different position, etc. then the accuracy decreases. Torque PMs aren't perfect either as their strain gauges depend on temperture which can drift throughout a ride. Also, as many of you probably know, I had issues with my first Quarq so it is important to check the calibration of any device.