An interceptor member for use in a position transducer comprises a substrate lamina (13) permeable by light or other radiation and barrier lamina (14) impermeable to said radiation. The barrier lamina (14) has annular window elements (13a1 - 13f) occupying one of a plurality of annular zones (12a to 121) extending about axis (11) of the interceptor member. Light or other radiation is incident through the window elements (13a1 - 13f) of each zone on respective photo-transistors (19a - 19f). The configuration of the window elements collectively is such as to provide a binary coded digital output which may be of Gray form. The transducer may be utilised in a method of checking vehicle axle loading or providing an output to operate an indicator or adjustment means for levelling vehicle head lights when the vehicle tilts due to varying loads.