Let's say for the sake of the argument that a person would burn 100 calories per hour sitting on a chair. That person does an hour of exercise on a machine at the gym and the display states that 600 calories have been burned.
Ignoring any inaccuracies in the way the machine does the calculation, does that mean the person has actually burned 600 calories by using the machine, or that they have really burned only 500 (since they would have burned 100 anyway "for free" without the machine's help)?
If the answer is that it varies between machines then I'd like to know what is most common (if such an answer is possible).