I did a test with a heart rate monitor.
Just working at my desk, I burn 181 calories an hour with an average heart rate of 72. If I use the elliptical, my I burn 267 calories with an average heart rate of 89.
That makes 79 extra calories
If i do it 4 hours a day, thats 344 extra calories, without changing my routine at all I can burn an extra 10.8 pounds a year