Notes: "The Hemmi 301 and 301A slide rules exist to simplify frequency response calculations in control engineering. From the manual: “Frequently in the field of automatic control engineering, mechanical engineering, electrical engineering, communication engineering, etc., it is necessary to computer the magnitude ratios of phase shift angles for physical systems subjected to sinusoidal inputs. This slide rule has been invented by Professor Keisuke Izawa of Tokyo Institute of Technology firstly in order to obtain the frequency responses of physical systems where the transfer functions of the systems can be broken into real linear and exponential factors.” The Hemmi 301/301A was also sold in the USA by Post as the model 1490. "
