Daily weight is mostly noise.

Both work, and it depends on how the number lands on you. Daily readings feed a better average but expose you to the noise every morning; weekly is calmer, though a single weekly reading is itself a noisy sample. What matters more is what you read: a seven-day rolling average of the same numbers turns an unreadable scatter into a visible trend. That's the single most useful change available in a weight journal.

Day-to-day weight shifts with fluid balance, salt intake, carbohydrate intake, hormonal cycle, digestion and sleep — and those swings routinely exceed the actual change across a whole week. So reacting to a single reading is largely reacting to salt. Keeping conditions consistent helps: same time of day, same clothing or none, after the toilet and before eating, same scales on a hard floor.

Yes, but where you put it decides what the journal becomes. Logged immediately beside weight, mood invites reading causation into coincidence and the page turns into a verdict on you. Record mood, energy and sleep as inputs that explain a week instead — and rate the day rather than rating yourself. The wording of that field is what determines which of the two you end up doing.

Fewer things than you'd expect. Weight is an outcome you don't directly control on any given day, so a journal of outcomes alone gives you nothing to act on when a week disappoints. Add two or three behaviour fields phrased as yes or no, and add sleep — short sleep reliably increases appetite the next day, which makes it the column that most often explains a puzzling week.

If it starts feeling compulsory, if a reading ruins a day, or if you change what you eat in response to a single number — stopping is the correct response rather than a failure, and that pattern is well recognised rather than a personal shortcoming. It's worth writing down in advance what would make you stop, because deciding that is far easier before than mid-spiral. If there's more to it, a GP is a route and eating disorder helplines operate in most countries.