Fitness Heartrate question

I am hoping one of you will be able to either answer my question or point me in the direction of someone that may be able to answer it.


Most pieces of exercise equipment will tell you how many calories you burn while using it. I also know that they are not reliable. However, I would think that if you use two different pieces of equipment and keep your heart rate in the same place on each of them that the calories burned would be the same. Your heart rate is the indicator of your exertion as far as I understand.

So on the Matrix I keep my heart rate in the high 130's for 40 minutes. (it asks for my weight as when I start) It says I burned around 300 calories. Today I used the Arc for 40 minutes and kept my heart rate in the high 130's. I would think the amount of calories should be about the same but it said I burned 600 calories in that amount of time. Again, I am not using that number to run out and eat more food. I'm just curious what formula they use to calculate the calories.