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A father and son team have developed a totally new calculator based on a natural 'pen-and-paper' approach to mathematics. Their invention involves writing on a screen or white board linked to a computer that recognises your handwriting and animates it into correct equations. 'It is highly responsive and extremely easy to use. People who use it enjoy working (and playing) with it', explains Harold Thimbleby. 'You have to see it to find out how much fun it is'. The invention lets you write normally in two dimensions, allows equations to be edited continuously and it solves for unknowns wherever they are.

'With a conventional calculator you constantly have to rework a problem and approach it from different directions, so that you can enter it in exactly the right way for your calculator', says Will Thimbleby. A very simple example is 4x 5. If you enter this on a calculator the answer you are most likely to get is 1 rather than 20, which is the correct answer. What you need to enter to get the correct answer on most calculators is 4 x 5 followed by ±before you press = last. 'Unfortunately 4 x 5 ±= isn't proper maths, so it's confusing', explains Will.

'It's a very simple example but it illustrates the basic problem of using calculators. And it gets much worse the more complex the calculations'. It is not just a problem of having to work out a way to approach a calculation on a conventional calculator. There are differences in what the same keys do on different calculators, and even simple buttons are not obvious in their use. 'The percentage key is a great example', says Harold. 'How many people know how to use it?'