Ryoichi Yazu and his Jido Soroban

The Jido Soroban (Automatic Abacus) of Ryoichi Yazu

In his short life the Japanese inventor Ryoichi Yazu (1878-1908) was mainly interested in mechanics of flight and in 1890s designed one of the first airplanes, but remained best known for his invention of Japan's first mechanical calculator.

Ryoichi Yazu was born on 30th of June, 1878, in the village of Iwaya, near Buzen, Fukuoka, in the family of a village mayor.

He attended primary and middle school in his home village and the city of Buzen. At the age of 16 he left middle school and moved to Osaka to pursue his interest in flight, studying mathematics and engineering at a private school.

At the age of 22 Yazu returned to Buzen and began work on a thesis on the mechanics of flight. It is believed, that at the same time he got the idea for the calculating machine while helping with his father's clerical work, and conducted research on calculating machines. Three years later he brought the thesis Principles of Flight and a model of his mechanical calculator on a visit to the novelist and army physician Mori Ogai. Very impressed, Ogai wrote recommendations that led to a special research position at the Tokyo Imperial College of Engineering, where Yazu worked on the design of a propeller-driven airplane.

In March 1902, Yazu applied for a patent on his automatic abacus and completed a version made entirely of metal. The patent (see the nearby patent drawing) was granted in January 1903, and in March a shop was established in Tokyo, where the first calculator in Japan (known as Patent Yazu Arithmometer) was manufactured. It was a manual desktop calculator with pin-wheel mechanism, which performed decimal arithmetical operations using a single cylinder and 22 gears with biquinary number setting (a mixed base-2 and base-5 number system familiar to users to the soroban (Japanese abacus)). Carry and end of calculation were determined automatically.

The price of Patent Yazu Arithmometer was rather high (¥250), but more than 200 were sold, mainly to government agencies, including the Ministry of War, the Home Ministry, the statistics bureau, and agricultural experiment stations, and also to big companies such as Nippon Railway. The profits from the sale Yazu invested into his airplane research.

Automatic Abacus of Ryoichi Yazu

The Automatic Abacus of Ryoichi Yazu (source: museum.ipsj.or.jp)

Automatic Abacus of Ryoichi Yazu

Ryoichi Yazu died from pleurisy only 30 years old, on 16 October, 1908, in Tokyo. Later his father tried to improve the machine and to resume the business, but had no success.