magic scale?

On Friday there s a health check in school. The doc has a new scale, that shows exactly how many percent of your weight is fat, and how much is muscles. But I dont get how the scale could “know” that?
Does anybody know how this works? Magic? Aliens?


It’s probably one of these:

[li]An infrared tester (such as these. These testers use the fact that fat cells absorb different wavelengths of infrared light than other cells to compute the fat ration in your arm, which can then be extrapolated to your entire body.[/li]
[li]Skinfold calipers (such as this one), that measure the thickness of a fold of skin at a certain place on your body. The thicker the skin fold, the fatter that part of the skin is, and this correlates well with your total body fat (although it’s not perfect).[/li]
[li]Underwater weight measurement (sorry, no link). Basically, you can compute your density (and thus, estimate body fat percentage) by weighing yourself in water.[/li]
[li]Bioimpedance scales (such as this one. This is probably what they have. It sends an electrical current through your feet, measuring your electrical resistance, and how it varies with frequency. Because of the properties of fat cells, you can estimate body fat percentage from the data.[/li]

Although biased, these links are good comparisons of the different methods:
Infrared vs. bioimpedance

Comparison chart of all methods


so it s not magic :frowning: