Casio has sold its one billionth pocket calculator. The company's first electronic calculator went on sale in 1965, and in the run-up to Christmas last year, the one billionth unit was sold.

"We are excited to announce the sale of the billionth Casio calculator as it is a sign of the confidence consumers around the world place in Casio products.

"Using the technology and experience we gained through calculator development, Casio has grown beyond calculators into new markets for watches, electronic dictionaries, digital cameras and mobile phones. We continue to create original products and provide technology that adds to people's daily lives and hope the next billion calculators are received as enthusiastically as the first billion."

Sales of pocket calculators have tailed off in the last few years. Now that the large majority of people own mobile phones and home PCs with built-in calculators, only people needing advanced calculator functions need purchase one.

Casio's 14-A relay calculator is on display at the National Science Museum in Japan, as a key product in the history of the development of the calculator.