In this study, researchers pit five different fitness watches against a metabolic calorimetry chamber, and measured estimated physical activity calorie expenditure.
So there you go, the calorimetry formula gave an absolute enthalpy change of 6.2 kJ, while Hess's Law gives a change of 5.67 kJ. So, why the difference?
Any way that we can figure out the change of heat between the products and the reactants will work just as well, and that's where calorimetry comes in.
When doing calorimetry, we calculate a change in heat by measuring a change in temperature, but as we've said a billion times before, heat and temperature are not the same thing.