how do smart watches and fitness tracker measure the calories you burnt throughout the day/exercise?

Question

They might tell you, you burnt 2000kcal today or 300kcal during this sport training. But how do they get these numbers?
And afaik studies showed that they are incorrectly measured. How do the experts check that the data is correct? I mean you need the real numbers but for that you used the smart watch (or similar device).

In: 1

Answer 1

Its never an actual true number, just a calculation. Based on the activity your weight and other factors it would calculate energy spent. Taking it to very simple terms its like calculating the energy or calories to move a weight from point x to point y at a certain speed. Depending on the activity there might be other factors, which consider experimental measurements to make the calculation as accurate as possible. But again, its only a calculation. Use it for trends, as a guide, but not as an absolute true number.