One of the most accurate treadmill calibrator is fellnr. https://fellrnr.com/wiki/Treadmill_Calibration What does fellnr write about the accuracy of different sensors in his NPE run review: https://fellrnr.com/wiki/North_Pole_Engineering_Runn_Treadmill_Sensor « “ Conclusion of the MRIS Treadmill speed measured with different methods – a science of it’s own and little is known about it. We miss numerical and statistical …