A method for measuring the impedance of a portion of a subject, by passing a known current provided by a current source unit between a first pair of electrodes contacting the skin surface of the subject. The measuring of a voltage with a voltage measuring instrument, between at least one second pair of electrodes contacting the skin surface of the subject when the current source unit is passing the known current through the first pair of electrodes calculating the bio-impedance of the portion of the subject based on the known current and the calibrated voltage.
