The Delta Leg is a non-invasive manual instrument for evaluating the heterometry of lower limbs without any load bearing. It consists of a bar with two orthogonal footboards: one is stationary, while the second moves along the longitudinal axis of the bar and is equipped with a pointer indicating the positive or negative numeric value of the heterometry on a millimetric scale on the upper surface of the bar. The “zero” value is set with reference to the stationary footboard. The precise structure of the instrument, the mobile footboard’s accurate sliding system and the millimetric scale allow fast and reliable measurement of the differences in length of the lower limbs with a margin of error of just a few millimetres.