Checking heart rate during tracked exercise affects the heart rate measurement

[Angeash]

Heart rate tracking issues on Sensa are well known so let me add another one. Checking my heart rate during exercise results in bizarre dips in heart rate, going from 161 bpm to 123 bmp within 5 seconds, then back up again. You can see 4 of those bizzare drops in the picture below. That can't be a real physiological drop. Why does checking heart rate affects the measurement I have no idea but it's clearly wrong. 

[t.parker]

It's more likely to be caused by the motion of your arm when you are about to look at the watch.

[Angeash]

I keep my arm with my watch on the bike when checking.
In any case, it is physiologically impossible to have a heart rate drop by nearly 40 bpm in 5 seconds and then go back up again by the same amount. That's clearly a problem with the tracker.