http://people.ece.cornell.e... Wearable devices have become a popular and convenient way of measuring biological metrics for fitness and healthcare. While heart rate and motion detection have been well characterized, the measurement of other parameters such as hydration and body fat have not yet been made commercially available in the form of wearable device. The current standard for calculating total body water body fat rely on a measurement of bioelectric impedance. While this method is effective and reliable, the need to pass current through the body at two separate locations makes it difficult to make the system wearable. Thus, it is commercially available as a scale. An optical system can be used to calculate the same parameters, and by comparing optical measurements to the bioelectrical impedance measurements, this provides the redundancy needed for a reliable output. By taking advantage of the known relationship between optical density and body fat, fat percentage can be easily calculated. The challenge of relating optical density to both body fat as well as total body water can be accomplished by multivariable regression.