Estimated Date: 1935
Name: Tonoszillograph of Prof. J. Plesch
Manufacturer: F. Steffan & Co.
Description: 6“d x 3.25“h steel case has a glass viewer on top with a plate with a pen. The plate holds a circular graph and the revolution and the excursion of the pen are controlled by air pressure from a port. A second port is also present and a dial marked A and Z to open and close the top. The whole is contained in 7” sq pine box, which also contains the cuff and the original instructions.
Reference 1: 404