According to the EatSmart Manual:
"The EatSmart Precision GetFit Bathroom Scale measures weight and uses bio-electrical impedance analysis (BIA) technology to estimate body fat, total body water percentage, bone mass and muscle mass in generally healthy children 10-17 years old and healthy adults. It is intended for use in the home only.
The GetFit Bathroom Scale uses BIA (bio-electrical impedance analysis) technology to calculate body fitness.
In bare feet, this technology sends a low-level electrical signal through your body and then measures the resistance the signal encounters. This signal is perfectly safe and will not be felt. The lower the body fat, the faster the signal will travel.
You will be given a final reading of your weight, % body fat, % total body water, % muscle mass and bone mass. This scale stores up to 8 different users’ personal profiles and will be able to recognize these users as soon as they step onto the scale, after the initial setup."