Excellent point. And this calibrating is a key point as you lose weight--once you drop a significant amount you've got to revise your calorie intake down a commensurate amount.
Estimation is good enough as long as you monitor your progress and tweak it if it's not getting you results.
This is the best explanation I've seen anywhere about why you sometimes need to provide the parameter name for the first parameter in a func and when you don't.
I have both an Apple Watch and a FitBit Surge. The Apple Watch is the better smart watch, but the Surge is a much better fitness device and you can actually see workout data in a meaningful way. At this point, I definitely need both.