Shown in simulator is recording head wiring.
Square wave is Morse code radio or other code signal. Two vertical SPST switches are bend up wires 1/32 inch or less apart with freshly coated paper tape coated with potassium iodide (from drugstore) being pulled underneath. When recording head circuit is on a small brown line is made on a paper which is cranked through rubber pinch rollers.
Full drawings are in 1932 May Popular Mechanics Magazine on page 826.
