Accuron 600

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In the first years of the 70s, there was a lot of competition in the production of the cheapest pocket calculators: japanese companies produced huge quantities of calculators with a capacity of six or less digits, but the National Semiconductor in the USA also entered this competition in 1974: their chip could be used to build the simplest calculator of all time: it was capable of displaying six digits, but it could not handle decimal fractions, so it did not have a decimal point key either. Like Hewlett-Packard machines, it used Reverse Polish Notation (RPN), but it didn't have a separate ENTER key, while it was replaced by the + key. In addition to its many shortcomings, it is worth mentioning that it handled negative numbers properly and also had a CE function to correct incorrect keyings: the C key deletes the X register of the two-level stack and replaced by the contents of the Y register.

National Semiconductor produced their own models built with this chip, which were the cheapest machines available in the U. S.: it costs only half of a standard eight-digit machine. The interesting thing about the first model (600) was that a switch could turn on a fixed decimal point after the fourth digit, so — since the machine still didn’t calculate fraction part — multiplications and divisions gave erroneous results. This feature has been removed from later models.

Using that chip, many companies have built six-digit calculators, such as the malaysian Accuron with model 600.

You can read more about this and competing six-digit models in our special article.