Unique 2-in-1 calculator app adds up to surprise hit for retired engineer in Japan

TOKYO -- A 63-year-old man in Japan who is an avid iPhone user has dedicated some of his post-retirement years to developing a popular, unique app that displays two calculators on one screen.

The two-in-one calculator app has been released for iPhone and iPad, under the name "Twin-Calc." Hiroyuki Ueda, who lives in Nishinomiya, Hyogo Prefecture, is the mastermind behind it. Though the app struggled to gain downloads in the beginning after its release, the number surged once he made a certain tweak.

The double calculator app allows users to move the computation results of one calculator onto the other by tapping arrow keys displayed on the middle of the screen. For example, if a user calculates "89 x 15 = 1335" on one calculator and taps the arrow key, the result "1335" will be displayed on the other calculator, allowing the user to continue a problem while the previous equations are still shown on the screen. This makes it easy to notice errors.

It is also possible to perform different computations on each calculator. This function comes in handy when the user wants to compare prices to determine which store product is cheaper by the gram, for example.

Ueda studied mechanical design at university, and worked mainly in engineering, including the design of transmission components, at an automobile firm for many years before retiring at age 60.

He was originally a great iPhone fan and took up learning the Swift programming language as he had time on his hands after retirement. He was finally able to realize his dream of giving shape to inventions he thought would be convenient.

Ueda directed his attention to calculators, as they are closely tied with people's daily lives and are a universal tool without any language barriers. He began working out the vision for the app three to four years ago, and started actually developing it in August 2021. According to Ueda, an app that combined two calculators on one screen did not exist at this point, and seizing this chance to make a one of a kind software, he aimed to develop apps for the iPhone and iPad.

However, Ueda recalled, "I thought it'd be easy, but it was unexpectedly hard." Difficulties arose when responding to cases of inputting numbers with decimal points. For example, while there are users who input 0.5 by tapping "0," the decimal point, and then "5," there are also users who only input the decimal point and "5," while omitting the "0." He said, "There were around 100 types of these sort of conditions, and it was a lot of work to solve them."

After trial and error, he was able to release the app nine months later in May 2022. The number of downloads grew at a sluggish pace at first because the app was designed so that just one calculator is displayed on the smartphone's vertical screen mode, while two are shown only when the screen is rotated on its side. So, many users only thought it was a regular calculator.

Ueda then made alterations so that the app is fixed on horizontal display and that two calculators are always displayed simultaneously after the app is opened. This renewed version was released on Aug. 18. According to Ueda, as of Sept. 8, there were about 56,800 downloads for the version that costs 490 yen (about $3), including tax, and some 5,000 downloads for the free version. The paid version had around 18,000 downloads shortly before the renewal, so the amount had more than tripled following the update.

He commented, "A surprisingly great number of people have downloaded the app. I think there is demand." The latest task he is working on is to respond to requests to display two calculators even on a vertical display screen.

Ueda, who says there are few people in his generation who are tech-savvy, commented, "I hope I can become someone who inspires others."

(Japanese original by Tsuyoshi Goto, Digital News Center)