Update:
Today avg. hr was ok, so maybe it was just a bad day.
Hello, i am using polar h10 with watch. When in activity the watch showes wrong average hr when running. after 2 km of running the hr should be like 135, but showed in the watch only 114. so i think maybe the watch calculate the average when connected to the polar belt. instead it shout calculate it from the start of the activity on. at least at the end the average seems right when i check the activity later on, for example with GC. Sorry for the bad english. Greetings