Both previous answers make some good points. And, it sounds like you have a pretty good approach to the matter to begin with. But, if all else fails or you need to really show someone what they are doing so they can see if they are going to achieve a deficit or end up in a surplus, you can try Bodymedia..
I even keep a couple around that I “rent” out for a week or two so people can see what they’re burning vs what they eat. Because it measures heat expenditure, it’s far more accurate than the motion based devices.