A person's weight can change during the day up to plus or minus 2-4 kg:
ate - gained grams;
went to the toilet - threw off;
slept - threw off or gained, it depends on how you slept.
we gain weight not only through the mouth, and we lose it not only through two holes.
Therefore, control weighing is best done once in week, and not after the curd.
Then the dynamics will be visible.
Any scales are checked using calibrated weights. The most correct scales are medical mechanical scales with moving weights. Of course, now there are good electronic ones, but they are not cheap. From experience I can tell that many inexpensive household electronic scales tend to give unstable readings. These are design flaws, mostly mechanical. The upper cup (rather, the lid in this case), which transmits pressure to the sensor, is slightly skewed and the readings are highly dependent on the position of the weigher. And with such scales, the movement of the lid from the weight is very small. That is why manufacturers definitely recommend that the scales should stand on a flat floor in one place, and usually it is even shown with pictures how to get on the scales correctly. In cheap scales and electronics are worse. We threw out the first electronic scales for the same reason, bought a better one. Really good scales must necessarily be aligned horizontally and have a position sensor, as well as be calibrated, but for everyday needs the principle "and so will come down" is applied, especially since it is understandable that the consumer will not bother too much. The advice here may be this: buy scales of well-known brands and follow the manufacturer's recommendations. Well, you need to understand that a person's weight fluctuates throughout the day, so you need to weigh yourself at the same time, however, this is also in the manufacturer's recommendations.