marsden MBF 6010 Manual page 23

Body impedance measurement methods
In the conventional 4-electrode method, current is supplied from the
electrodes at the tips of the toes on both feet, with the voltage
measured on the heel. This current flows from one lower limb
through the lower abdomen and then into the other lower limb, and
the bio electrical impedance (hereinafter, impedance,) thus
measured is the impedance between the two feet. For reference, the
impedance measurement methods for the legs are shown in the
diagram below.
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