I'd completely disagree with Bill that it's even within the realms of possibility. It's not.
Exercise is generally between 6 and 10 calories per minute (cpm). Hard exercise, especially if obese, can produce higher, like maybe 12, possibly as much as 13 or 14 for an especially conditioned obese person (fit and fat) who is really pushing it.
This value offered by Spark is 20 cpm.
That is NOT even within the bounds of realism. Not possible. For anyone, anywhere.
Please read this blog on the exercycle where I test Spark's calculations to discover that for magnetic resistance machines (of which elliptical is one too) that don't actually use your bodyweight, Spark is factoring your bodyweight, producing fantastically impossible results: www.sparkpeople.com/mypage_public_journal_
If you don't have an HRM to use, see what the machine itself offers, if it does, or google other sites for an approximation. Do not use Spark's entry.
I wish they'd remove it or change it. It's so hopelessly beyond the bounds of possibility. It's horribly overcalculating for some people, especially if they use that machine a lot and rely on Spark's figures.