How does the body monitoring scale measure your water percentage, fat percentage and muscle mass?

I mean, is the info reliable?..cos you only step on it with your feet, so how does it know all those percentages in your body?

Public Comments

1. it sends a small electrical current through out your body. all parts (bone, muscle, fat, water, ect) impede the current at different rates so the "speed" the current goes through your body determines the percentages. the accuracy is +/- 3% of the skin fold measurements (which has a+/- 3% error), there are some limitations such as proper hydration, its not accurate for pregnant women, etc