The scale said 93.1 kg on Monday and 94.2 kg on Thursday. Same person, same deficit, a kilo gained in three days. That number is not fat. It is water, glycogen and salt moving around, and it can swamp a week of real progress without a single calorie of surplus.
What actually moves the number
A gram of glycogen binds three or four grams of water, so a hard ride that empties the tank can drop two kilograms by morning — and refilling it puts them back just as fast. A salty restaurant meal does the same from the other direction: sodium holds water, the scale jumps, and nothing about body fat has changed.
Hormones add a slower wave. A bad training block or a short night shows up as a two-to-four-day bump that looks exactly like a plateau and is not one.
The rule I read by
The only number I trust is the seven-day rolling mean of the morning weigh-in, read as a slope. Day to day the raw points are weather; the mean is climate. This site draws both — the dots are honest, but the verdict on the home page comes from the mean, and the weight chart shades a ±0.5 kg noise band around the trend so a stall has to be real before it counts.
A real stall is the mean sitting flat for two weeks or more. Anything shorter is the scale lying, and the right response is patience, not a panicked cut.