Heart rate monitor Vs The one on the treadmill..... which is

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I do the lesilie samsone dvds and burn about 500 cals in 45min but I got on a treadmilll last night for a half hour and only burned a bit over 200cals I did 3 mph and a 5 incline. It seems like I was doing more work on the treadmill but burning more cals with the dvd. could that be right?