I had the opportunity to supervise this at a competitive invitational and was not thrilled with what I saw. I had teams spending upwards of 15min fumbling around with the calorimetry lab (can't light the match, can't keep it from burning itself out, can't light the food, can't burn the food completely, can't burn the food adequately...) that's, still, only worth 15% of the score. It's not worth it! If you take the test very well, you're bound to win most levels of competition with or without the lab. I worry about how much practice time gets devoted to this activity.
Does the 15% of the score derive completely from the final determination of the calories in the food item, or are there a bunch of points divided up and awarded for things like setting up equations, unit conversions, error analysis, etc?
I think the calorimetry math, and being able to estimate energy losses, is all good stuff and worth studying and preparing for. Has this been taken into account when scoring the tests at the various invitationals that have happened so far?