Tadao and Toshio soon found themselves working all day on subcontracting work to make a living, and then spending their evenTadao and Toshio soon found themselves working all day on subcontracting work to make a living, and then spending their evening hours absorbed in developing the calculator.ing hours absorbed in developing the calculator.
They showed the prototype to people and then made improvements after getting feedback, and in this way worked out the various problems and bugs in the invention.
After making ten or more prototypes, they completed Japan’s first electric calculator in December 1954.

In 1955, the Kashio brothers proudly took their finished product to Bunshodo Corporation, the trading company handling office supplies, including calculators. Unfortunately, the Bunshodo representative told them that their calculator was out of date because it could not do continuing multiplication, wherein a multiplication product could be subsequently multiplied by another number.

Tadao and Toshio once again began spending their days working out the problems with the next prototypes. Around that time, both younger brothers, Kazuo and Yukio, also quit their jobs, and began working at Kashio Seisakujo. Toshio came up with the ideas, Yukio, who had taken mechanical engineering at university, drew the plans, and Tadao and Kazuo did the production.
In 1956, six years after the start of development, they were close to completing a calculator with a continuing multiplication function, and all they had left to do was figure out how to mass-produce it. At this point, Toshio suddenly stated that he wanted to completely redesign the calculator. The solenoid design with its complicated mechanical structure meant potential difficulties for mass production. Toshio wanted to eliminate the solenoid design and use relays like those employed in the telephone exchange equipment of those days, in order to make a completely electric calculator.
Although computers using relays had already appeared by the late 1950s, they were so large that they required a whole room to themselves, complete with an air purification system. The disadvantage of relays was that they were easily affected by fine particles and dust. In order to solve this problem, special ingenuity was needed to bring electronic calculation to regular offices.
First, the four Kashio brothers worked to reduce the number of relays from the several thousand (sometimes over ten thousand) used in the giant computers of the day to just 342, through improvements in the circuit design. They also developed an original new type of relay that was hardly affected by dust.
At the end of 1956, the brothers decided to unveil their completed calculator in Sapporo, but they ran into a snag when taking the calculator to be loaded onto the plane at Haneda Airport. The person in charge told them that it exceeded the allowable size, and asked them if they could detach the top part. The brothers turned pale. The top part included the display and keys, which were very important for the operation of the calculator. They tried to protest by saying that the calculator could be irreparably damaged, but finally took the machine apart for loading. After arriving in Sapporo they put the calculator back together, but just as they had feared, it no longer worked. They tried in vain to repair it, but it was completely unsalvageable. Although they went ahead with the presentation using slides, it seemed to end as a failure.

Just as the brothers arrived home, somewhat discouraged, a representative from Uchida Yoko Co., Ltd., paid them a visit and asked to see the calculator. The branch manager who had seen the presentation in Sapporo had told his head office to investigate the new invention. Since Uchida Yoko had subcontracted work to Kashio Seisakujo in the past, the company already had confidence in the Kashio brothers.
Now seven years of hard work in development had suddenly paid off. A contract was signed with Uchida Yoko as the exclusive dealer

The greatest feature of the four brothers¡ new invention was the adoption of the ten-key format. The calculators at that time used what was called a “full keypad” with just the numerals 0 to 9 for all the digit places. This newly developed relay-type calculator used only 10 number keys, just like pocket calculators today
A unique design was also adopted for the display. Calculators at that time had three display windows, and when calculating “100 + 200 = 300” the numerals “100,” “200,” and “300” were all displayed at the same time. However, with the relay calculator, the numbers disappeared after the next number was entered, and just the final answer appeared at the end. Today this seems like common sense, but at that time it was a revolutionary new idea, and it required a lot of hard work to get it accepted. With these innovations however, compact calculators were realized, and the office calculator was born.
June 1957, Casio Computer Co., Ltd., was established as the development and production company for the relay calculators. The brothers asked their father, Shigeru, to fill the position of President, which he accepted.
June 1957: World's first compact all-electric calculator, the "Casio 14-A" begins, and Casio Computer Co., Ltd. is established.