>But ultimately, if you miss 100 calories a day, and are in a 500 calorie deficit recorded, you are still going to lose .8 pounds a week. And if that is consistent, adjust your portions and be fine with how you record.

And the thing is, you'll need to do this anyway - because you can't be sure in advance how many calories represents a "500 calorie deficit" for you, in your specific current conditions.

I was quite underweight in my youth, but I successfully reversed these kinds of feedback techniques to gain weight, and currently maintain what seems to be a healthy level. John Walker (co-founder of Autodesk, who passed away early last year) wrote The Hacker's Diet describing the basic technique. It's still live at https://www.fourmilab.ch/hackdiet/ .