Measurement of the size and composition of a lymphoedematous limb. The limb is inserted into a vertically- or horizontally- orientated frame that emits two parallel arrays of infra-red light beams at right-angles to each other. The limb casts shadows that are sensed by receivers on the opposite two sides of the frame to the light emitters, and two transverse diameters of a 'slice' of the limb are measured. The frame is moved along the length of the limb, enabling similar measurements to be made every 3 mm. A circular or elliptical cross-section is assumed, and volume calculated accordingly. Limb volume, percentage difference between selected measurements, contour, and cross-sectional area can be displayed. It is difficult to measure the most proximal part of the upper arm or thigh, and the Perometer cannot measure the hand or foot accurately; further disadvantages are its large size and cost. The Perometer has been recently modified to enable detection of convex contours of the limb surface (the '3D-LED-scanner system'). Volume is calculated from a large number of diameter measurements instead of just two at right angles, but it is not necessarily more accurate than the earlier version.