So I'm a few days into using the watch for my gym workouts (weights not cardio) and I've noticed sometimes that the heart rate seems off. For example I was doing squats and expected it to be around 120-130 bpm and it was 112. I quickly swipped to calories and total time and back to heart rate and then it has jumped to 123. So is it actually accurately measuring it in the background but not always refreshing the data on the screen? BTW I'm in the default watch fitness app and using 'other' as there is no resistance training option.