How does the fitness tracker measure calories burned? Mine always require to know my bodyweight so that they can approximate the amount of calories burnt by calculating the energy needed to transfer the specific amount of meat via locomotion. I don't think measuring the heart rate would be a useful proxy either. I think the only reasonable way to properly mesaure the amount of energy used by playing chess would be to measure the amount of CO2 that's exhaled during a game and at rest and compare that.