Your scale and how to use it
"When and how should I weigh myself?" In a way that makes the number comparable with last week's, and then in a way that stops any single number from mattering.
Conditions
Same scale, on a hard floor, in the same spot. Same time — morning, after the bathroom, before food or drink, in the same amount of clothing or none. A scale accurate to a hundred grams is plenty; the day-to-day noise from water is ten times that, so a more precise scale measures the noise more precisely.
Frequency
Regular self-weighing is one of the most consistent habits in the research on weight management: a systematic review of prospective studies finds it associated with more weight loss and less regain in adults, without harm to mood or eating in the general population. The review is honest about two things. "Regular" meant anything from daily to weekly across the studies, so the rhythm is yours to choose; and the finding is an association — people who weigh regularly may differ in other ways — not a proof that the act itself causes the result. Daily gives the smoothest trend; weekly is enough for most decisions. What matters is that it is a rhythm and not a mood.
Trend, not reading
A single morning is water, salt, glycogen, gut contents and the cycle, in a band of a kilogram or two; the scale-jumps page lists the causes. The unit of information is the trend: a weekly average, or a smoothed line, over two or three weeks. That is what the app plans from, and it is the only thing worth having an opinion about. If a reading can change your day, stop looking at readings and look at the line.
When not to weigh
If weighing brings anxiety, restriction or a sense of being judged — and especially with any history of an eating disorder — the review's reassurance about the general population does not apply to you, and a clinician's approach that is not built around the scale is the right one. Waist, clothes, strength and how you feel are also measurements, and for some people better ones.
In the app
Weight entries feed a trend weight, and the trend is what the target is recomputed from; the progress page shows both, so a Monday spike is visible for what it is.