Casio, a Brief History of the Electronic Calculator
 

Tadoa had a younger brother Toshio, who was creatively gifted with extensive electrical knowledge. Tadoa from an early age admired the pioneering efforts of Edison, who invented the light bulb, and always told his family that he wanted to become an inventor.

While working at Kashio Seisakujo on the contract work underwater, and Toshio Tado invested heavily there the evening time development of the calculator.