This was Hitachi's first digital computer, developed to calculate the sag and tension of power transmission lines. It was completed in 1957.
The transistors of the time were the point-contact type, with large variation in characteristics, low production volume and a high price. Parametrons, in contrast, were determined to be inexpensive and highly reliable, so it was decided to use them as the logic element. A magnetic drum was used as the memory unit because it was thought to have the best future prospects at the time.
Machines like the EDSAC and ILLIAC were used as reference in the system design, but a number of innovations were also incorporated, such as an address change system using instruction addresses, and a system to facilitate bootstrap initial input by providing control codes on paper tape. The system was used in the design of power transmission line sag and tension for the Tadami Trunk Line of the Electric Power Development (J-POWER). Calculation time was approximately one minute per span, and it took about 50 minutes to print results. Doing the same calculations by hand required about 7 hours＊：Preserved at the Hitachi Central Research Laboratory