Since I don't run outdoors in the winter, I have not been able to calibrate my HRM Pro. I am however surprised that its ability to guess running pace on the treadmill is significantly worse than the FR255 without any running dynamics sensor.
When I jog 10 km/h, the HRM Pro indicates 11 km/h.
When I run 18 km/h, the HRM Pro indicates 12 km/h.
When I run 25 km/h, the HRM Pro indicates 16 km/h.
I hope it gets better with calibration.
I also wonder where the calibration is stored. On the HRM Pro? On the watch? In the Garmin cloud?