I have done eliptical in the past at a level 5-6--which is a moderate pace. My reading would be around 300 most days. I guess it depends on how hard you work. I don't think those things are terribly accurate anyway.
If you really want to know I think a heart rate monitor is the only way to go.
I let the TDP estimate my caloric burn for my walks to school - I put in my pace (which I know because I know the distances to where I'm going and can time it) and the minutes it took me and it figures it out for me.
I'm sure I would be much more accurate with a heart rate monitor but so far I'm still losing weight at the pace I expect using the estimates so I'm ok with it. If I stopped losing I would try to get more accurate to troubleshoot the stall.