It's my understanding that a heart monitor accurately measures calories burned. They aren't very expensive and well worth the money. When I first started working out regularly, I wore it religiously to make sure my heart rate stayed in the most efficient calorie burning range. Loved it as a motivator!!
Move more, eat less. Move more, eat less.
"What am I on? I'm on my bike working my a$$ off, what are you on?" ~Lance Armstrong~