A circular slide rule consisting of two concentric plastic circles which can be rotated with respect to each other and a rotatable cursor that allows a number of readings to be made. This device, called a Radio Transmission Line Calculator, or more commonly a Smith Chart, in honour of its inventor P.H. Smith of the Bell Telephone Labs., was first put into use around 1937.
It was used near radiofrequency devices to predict and confirm the transmission properties and the sizes of the radiofrequency waves of the emitted radiation from a transmitter. Detailed instructions as to the use of the calculator are included on the reverse face of the device. It measures 23 cm in outer diameter. Initial versions were produced by Bell Labs. This version was manufactured by Emeloid Co. Ltd. of Hillside N.J. in 1944.
The artifact was used primarily by personnel in the Accelerator Physics Branch at Chalk River where large radiofrequency power sources were installed.
