The pulse shows just awful. What happens in a sitting position the pulse 200, but it happens in sprints 140. Have tried everything I can think of: 1) Tightened the strap 2) the bore in the other arm 3) to flip the watch 180 degrees 4) gave the watch to another person. It did not help. Please tell me they can (optical heart rate monitors) and should work. If possible could you share your results for comparison work. Forgot to say I have a Tomtom runner cardio white red. Thanks in advance.