I have found a great difference among several fitness monitors. I have done an experiment to show you the differences. I walked a particular route every day for 3 days. It's a circuit around my park which is 2.5 miles long. There is a very steep hill on one side and another smaller steep hill on the other side. I tried 3 different methods of tracking my calories and here is what I got: 1. The Apple Watch Exercise App with Polar Bluetooth Cheststrap---284 calories 2. The Apple Watch Exercise App with its own (wrist) heart monitor (no chest strap)--288 calories 3. The iPhone with Digifit App and Polar Bluetooth Cheststrap---503 calories So, which one is right and how do you account for the differences? Did I do 284 calories of exercise, or did I do 500? What do I add to my calories for the day with each set up? P.S. Usually with the chest strap and other devices (like the Polar Loop) I come up with numbers closer to the Digifit numbers than the Apple Watch numbers, in other words a lot higher for the amount of exercise. Fooling yourself isn't a good thing but neither is working harder than you need to.