Abstract: A multidetector is constituted by a lattice of N rods each having a ferromagnetic portion and slidably mounted within N coils forming the secondary windings of a transformer, each detector being constituted by a rod associated with a coil. The common primary circuit of the transformer is formed by a single coil which surrounds the N secondary windings and is supplied with alternating current of constant amplitude. The rods are brought into contact with an object for taking an impression of a portion of its external surface. The N voltages developed at the terminals of the N secondary coils are transmitted sequentially by a multiplexer to the screen of a storage oscilloscope so as to form the impression by means of N points, a coordinate of each point being a linear function of the voltage developed at the terminal of the corresponding secondary coil.