HRM issues?

I don't understand my HRM. I have done the same workout 4 times this week for the same amount of time...with the same average heart rate. The past 2 days it says I burned 200 more calories than the first 2 days...how is that possible? On Monday it said I burned 383 calories in 34 minutes with and average heart rate of 168. Tuesday and Today I did the same work out for 34 minutes with an average heart rate of 165 and 162 respectively and I burned 571 calories on Tuesday and 558 calories today.

Could this be right?

What brand and does it have a chest strap?

I can’t answer your question but I had similar issues with my polar watch. I couldn’t get a correlation between average heart rate and total calories. I am thinking it calculates calories burned as you go and even though the averages are the same the relationships are non-linear so you would get different results if you did all 34 minutes at a constant 168 compared to doing intervals where the heart rate is going above and below 168.

I use my daughters old power meter from her bike and I found that the results from this method are more consistent. When I ride my bike, in addition to measuring time and heart rate, this measures how much work I am doing. When I compare this to my polar, the polar gives me a higher value for calories burned. So when I enter my workout into the log I only count 75% of the calories my watch reports.