calories burned during exercise?

I know that the estimates these cardio machines give can be way off. Is
there any way to get a relatively close idea how many calories I am burning?
At any rate, I have an elliptical in my basement, and although I don't use
the calorie meter as an absolute, I have been trying to work past the
previous calories burned each time I work out. This just gives me a little
motivation to push a little harder each time.

My elliptical shows that I burned 400 calories in 35 minutes. This is at a
high resistance and at a fast tempo. Is it remotely possible that I am
burning that much?

Betsy