An Irish father and daughter duo had a special reason to celebrate the New Year, when their calculator app they invented hit the top of the Amazon Kindle Fire charts.

Adrian and Isabel Hughes worked together to develop Calculator Plus, which is now the number one calculator app for the Kindle Fire tablet in the US and UK. It is the second highest rated app on all categories out of a total of 64, 878 apps on Amazon Android store. They reached one million copies downloaded on December 29.

USA Today recently named Calculator Plus as one of their 25 essential Kindle Fire apps and Amazon are now pre-installing it in all of their shop demo models across the US.

Their Windows 8 version, Calculator Free, is already the most downloaded calculator on that platform after just a month.

Calculator Plus is now available in Ireland for smartphones from the,Google Play Store and the Apple App Store by searching under the, firm’s name, Digitalchemy.

“The beauty of the new Calculator Plus app is that it remembers everything you calculate, which makes it perfect for running a bunch of tasks in tandem over a long period of time,” said Aidan.

“Again it came from Isabel and I bemoaning the fact that you lose everything when you turn a calculator off.”

And for iPad, Aidan and Isabel have two apps: Easy Fraction Calculator, with beautiful backgrounds, and Fraction Calculator Plus that includes a handy ruler for woodworkers.

This is the second success for Dubliner Aidan and his daughter Isabel, 13, who have invented a unique way to work with fractions.

Fraction Calculator was conceived by the duo while Isabel was doing her maths homework in Seattle, Washington.

“After a page of checking answers to fraction problems, we were both exhausted!” said Aidan, 41, originally from Raheny.

“I knew there had to be a better way, and I thought of a fraction calculator with three keypads that would be fast and easy”.

The app has two great features not found elsewhere: An innovative three-keypad layout to enter fractions and a large, easy to read, display that shows fractions the way you write them.

Fraction Calculator was recently released on the Amazon Kindle Fire, where it rapidly rose to the number one paid calculator spot. It’s been in the top five ever since.

Hughes began his foray into the world of computers at the age of 12 by programming a baking game for his brother Kevin, who suffers from epilepsy.

After leaving school early, he got a job at Clontarf computer company, Fred Crowe Limited, where his first task was putting Irish plugs on US computer cords. By the age of 20, he was the senior programmer at the firm.

A year later he started Digital Alchemy and went on to create software for Irish firms, the Irish Government, the United Nations, and various US software companies.

He joined Microsoft in 1999 as a software developer in Seattle and registered more than 20 patents for inventions in computer security.

In his last role at Microsoft, leading the PM team for the forthcoming Windows 8 Store, he felt the entrepreneurial urge, and left to start app development firm Digitalchemy.