By giving a sinusoidal waveform to the Y input and a cosinus waveform (which is made by a 90° phaseshifter from the sinus generator output) to the X input of an oscilloscope or graphic plotter you can generate a circular rotating point on a XY coordinate system. The rotation frequency is given by the sin/cos generator. Using a high frequency this point will be visible as a circle on the oscilloscope, by using a low frequency it will be able to draw a circle on the plotter.
This circle can be formed and modulated by another signal, e.g. a triangle wave like in the scetch. This modulation signal can be synchronized with the circle generator, in our case the frequency of the triangle generator is 12 times higher than the frequency of the circle generator – with the result of stillstanding star-formed pictures.
The complete machine is consisting of the circle generator, which outputs can be “frozen” at any point of the circle by a Sample+Hold circuit; the input part, where one of four different XYZ inputs can be selected; and an analog electronic calculator which is processing an XY coordinate system rotation algorithm with the selected inputs.
Besides this main circuit, the instrument contains several VCOs, counters and phase-locked loop circuits, staircase generators and a grid pattern generator as well as some smaller elements like amplifiers etc.. These individual parts can be connected together via banana plugs to realize various ideas of switching.