Presumably, with each calibration garmin sends crank length to the power meter. I realized, that despite the setting on the watch, it is sending some weird values. The only time when it sends right values happens when you set the crank length on the watch. With setting I mean CHANGE. So if you are using 172,5 you need to set something else, than change back to 172,5 and calibrate. With next calibration it will send 180... And I didn't manage to check when it happens, but finally it sends 208mm! Difficult to troubleshoot. I am using favero BePro, so I am able to check the crank length via PC. Check your power meters, because your good power results this year may be caused by this bug...