: Big difference in Heart Rate Monitor meassures I've always ran with a Polar HRM sync'ed with my Nike+ SportWatch. I recently got a Microsoft Band 2 and I noticed the avg HR for every run have big differences. I'm a 38 yo

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Reading heart rates accurately can be a tricky thing. The bands and watches use a little bright light that flashes really fast to read blood density changes in the veins of the arm and wrist. Chest straps read electrical signals in the chest. Chest straps tend to be more accurate than light sensors. Light sensors (I've found) tend to lose a lot of accuracy as the heart rate goes up. Another common issue that can effect reading of light sensors is other light that may seep in between the wrist and band. The band has to be firmly on your wrist and not shift around otherwise it's going to effect the reading. Same for Forerunner 225.

So I don't know which Polar HRM you used, but my guess is it's a chest strap one (I'm not sure if Polar has any other kind). The Microsoft Band uses light. I used to have a Basic watch which would not be able to read heart rate faster than 130-140 bpm. Microsoft may have some way of compensating for the inaccuracy in which case it seems to be shooting way passed target.