Like most household body fat scales, the Fit Plus Smart Body Composition Scales use the Bio-electrical Impedance Analysis or Bioimpedance Analysis (BIA) Method to assess body compositions. Measuring body fat in relation to lean body mass, it is an integral part of a health and nutrition evaluations. This non-invasive test simply involves your feet touching four electrodes on the scale. A low level, imperceptible electrical current is sent through the body. The flow of the current is affected by the amount of water in the body. The device measures how this signal is impeded through different types of tissue. Tissues that contain large amounts of fluid and electrolytes, such as blood, have high conductivity, but fat and bone slow the signal down. As BIA determines the resistance to flow of the current as it passes through the body, it provides estimates of body water from which body fat is calculated using selected algorithms. It is why the measurements need to be done barefoot, with user’s both feet on the scale touching the metal pads.