A geometric model construction system comprised of a variety of shape elements. The swing arm assemblies extend along vertical faces of a frame and are adapted to rotate the bar from one position between the vertical faces to another position. A spectrum display may be superimposed as a third dimension on a two-dimensional tuning field with one axis representing the frequency, the second axis representing tuning resolution and the third axis representing the signal level. Magnetic materials, which are formed on the insulated resin layers, sandwich the coil pattern. A proximity sensor may also detect the presence of the computer user by detecting the weight of the user at a location proximate the computer.