I have been using the HRM Pro chest strap for the past 2 years. Because it now smells horribly, I bought the HRM Pro Plus. However, it seems to work differently. I already had a too low heart rate during the first run, then intermittent dropouts (disconnected from the watch). I returned it and got a new one. Today, while running on the treadmill, the heart rate was clearly too high (about 10 beats too high). I then switched to the old strap in the middle of the run, and the heart rate returned to normal. I was always running the same pace on the treadmill. (I've attached the heart rate measurements from today's run, you can see where I switched the strap)
What could be the reason for this? Is there a different system behind it, or why am I suddenly getting incorrect readings?
