I followed up my comparison of the Band vs RunKeeper on the iPhone by switching the wrist I wore the Band on. Moved it from left to right wrist. As I am right-handed and my right wrist has greater circumference than the left, the Band seems to fit a bit tighter but was always fairly tight on left, too. So .... for essentially the same run I got hugely different calorie counts from the Band. The results with Band on right wrist were about 60% of those on the left wrist. And heart rate was similarly lower on right-side. Whatever Microsoft is doing to try to measure the heart rate -- which this thread says is then used to estimate calories burned -- seems to be very undependable and misleading. So much so that their advertised promise of " Microsoft Band ... helps you achieve your wellness goals by tracking your heart rate, steps, calorie burn, and sleep quality." is really not true nor honest, IMHO. I am pretty disappointed. I did not expect 100% perfection but this level of performance is beyond being what Microsoft should find acceptable.