How accurate are crosstrainer/elliptical calorie burners?

I'm about 5'0/5'1 and weigh around 103 lbs. I'm trying to get to 95 lbs, with an extremely low metabolism from a restrictive diet of 600-800 calories for about two/three years. I've recently gained about 8 lbs from binging and it's all excessive flab :(

Anyways, I have an Octane cross trainer that has a pretty heavy resistence, even on level 1. I put it on level 2, which has me panting and sweating, and I go pretty fast - it says I burn about 700 calories an hour, is that accurate? I do around a half hour each day, or try to. And I also enter my weight in as 90 lbs.

My gym's Lifestyler Ellipticals (I like) and Treadmills (I hate) seem pretty accurate. Not sure about the bikes.

A half hour on the Elliptical at 85% of cardiac maximum gets me close to 300 calories...and I believe it.

But as long as they have a TV set on them I'm happy.

How accurate? Probably not very, unless you just happen to fall into the "average" profile upon which its formulas are based.  But regardless of accuracy, it's still quite helpful as a way of comparing how hard you are working during the workout and from one to another. 

Just don't expect to use that number upon which to base your total calorie budget and calorie deficit to obtain the standard one pound loss per week.  If that works, then great, you probably do fall into the average and it's reasonably accurate for you.  If not, you'll have to experiment with different "deficits" for a while, until you find the one that actually produces that 1 pound.  From there, you can probably calculate approx how much the burn really is (assuming that your calorie intake measurements are reasonably accurate.)

Or, just get a good heart rate monitor.  That's a far more accurate.