reckoner
It is a fair thing to check before you start taping yourself. A number you hand a piece of software is usually a number it acts on, and a plan that quietly reshaped itself around your waist would be a plan you could not predict from one month to the next.
So the four girths are held apart from the plan on purpose. Waist, chest, hips and upper arm are marked as figures the generator is not given, alongside your age and your height. They are stored, they are drawn on their own pages, and they stop there.
What does reach your program
It is a narrower rule than it sounds, and the narrowness is the point. Reckoner is not refusing to look at your body. It is refusing to let a figure you took with a tape measure in your own bathroom, once a month, under conditions nobody can check, silently outrank the record of what you actually lifted. One of those two is evidence about your training. The other is evidence about your shape, and they answer different questions.
Your bodyweight, and it is the one figure here that does two jobs. Strength standards are relative, so a bench press means one thing at sixty kilos of bodyweight and another at ninety, and the calibration that sets your opening loads reads your weight for exactly that reason. Your fuel targets read it too, which is why correcting a current weigh-in tells you your targets are moving.
What lifts you and what loads you is your logged training and nothing else. The sets you finished, the reps you got, the effort you reported. That is the whole of the evidence the engine reckons from, and it is why the reason printed beside every decision is always a sentence about a session rather than about a body.
The practical consequence is that you can tape yourself badly, or not at all, without costing yourself a single kilo of progression. A month you skipped changes nothing about next week. A reading you took with the tape too tight changes nothing either. The worst it can do is mislead you, which is a real cost and a different one, and it is why the guide below spends most of its length on taking the measurement the same way every time.
It also means the reverse. Your figures cannot earn you a lighter week, cannot trigger a swap, and cannot explain a stall. If your waist is coming down and your bench is not moving, those are two separate facts and the software will treat them as two separate facts. Reading them together is your job, and it is the one this record exists for.
That is the short version. The whole decision, with the numbers, is in How to take body measurements that tell you something.