A device for simulating electrical characteristics of an electrical, electronic or electromechanical component comprising circuitry (21) adapted to reproduce electrical characteristics which are produced by, or may be sensed in, the component, the device (1) being configured so as to substantially resemble the component in appearance and/or size. The device may have two substantially flat opposed surfaces (3,27), one of which carries a picture (5)of the component and the other a sectional view through the component to illustrate its technical construction or operation, and/or other data relating to the component. A kit may be provided comprising a number of such devices each to simulate a component forming part of an equipment or system so as to simulate the electrical characteristics and/or performance of the equipment or system.