The Museum of HP Calculators

The Friden SRW

By the 1950's, four function motor driven mechanical calculators had become common on the desks of engineers and scientists. Most of the models sold in 1950 looked a lot like the more advanced models of 1915 with Friden and Monroe selling most of the units. In 1952 Friden shook up the market with the SRW. The new model looked very much like the Friden STW on which it was based but it added the amazing ability to extract a square root at the touch of a single key.


The Friden SRW was an imposing calculator weighing 42lbs. The carriage contained two registers. The upper register showed totals, subtotals, products etc. The lower register showed the number of items added or subtracted, multipliers, and quotients. (There was a third register for multipliers on the keyboard.) The keyboard contained well over a hundred keys including both full and ten key keyboards.

Extracting Square Roots

To extract a square root, the user could simply enter the number on the keyboard and then press the square root key at the base of the keyboard that corresponded to the position of the decimal point. The machine then produced the square root using a clever algorithm within a few seconds.

Picture of a Friden SRW
Small (60K)
Large (150K)
10 second exposure of the SRW extracting a square root
Small (54K)
Large (147K)

This is one of three running SRWs that the curator knows of. If you know of others, please send a message.

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