Was there life before computer?

calculating instruments before the digital era

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Virtual HP-35

This calculator in 1972 marked the end of slide rules, still practical and usable. The HP 35 tore each record, the volume of sales was 10 times higher than expected, despite the price, and for its diffusion rate was dubbed "the slide rules killer". With the push of a button you will instantly perform all the trigonometric and logarithmic functions and the display, red LED that limit battery life to 3 hours, calculates up to 10 decimal places. The time to look for interpreting the results was ended and analogue scales could not survive.

The name 35 derives from the number of keys but in the first series was not reported, needless to characterize a product in the absence of competitors! Its operation is special: it uses the logical principle of Reverse Polish Notation (RPN), designed in the '20s by Jan Lukasiewicz, which allows to describe any formula without the use of parentheses. Before you enter the operands and then operators: (4 + 5) x 6 becomes 4 ENTER 5 + 6 = x and therefore lacks the key =. The RPN eliminate the problems due to parentheses and operator precedence (first division, then the addition etc..). To make a simple example try to find the hypotenuse of a right triangle with legs of 3 and 4 cm, actually easier than with a slide rule: first the calculator must be switched on clicking on the switch located in the upper left, then you can use as normal but when you ahave finished do not forget to turn off the power: the batteries last for a very short time.


The Java animation was done by Neil Fraser: from his website you can download the code and from this link the standalone program.

The 35 is always sold as HP 35s. Of course today the display is digital but the calculator still retains all the characteristics of a time, including the reverse polish notation. Only the logo is different: it is shown in plain sight because today certainly does not lack competition ...

The current HP 35s: its operation is similar to the model of 1972

No name for the first calculators: were only "electronic slide rules"

Nicola Marras 2008

Credits: Neil Fraser


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