from experience I know I can ride for a long time day after day on about 1 scoop of perpetuem per hour.
just by having something that actually calculates calories, is a boon. i suppose about as useful as an inaccurate gas tank gauge or a compass thats not declinated correctly.
its a measure, something to go by.

somewhere at some point I think I read that you can only assimilate about 300calories per hour.