Hand-held Calculators

Hand-held Calculators

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The devices that ended the three hundred year supremacy of the logarithm table. Early examples were comparatively power hungry and had a very limited battery life. They were frequently used with mains adaptors. The development of low power integrated circuits and in particular, liquid crystal displays meant that calculators at last became truly portable.

Top row, from left to right

• Rockwell 24RD-II - (1976). Six functions (+ - × ÷ % √). This has a 9 digit fluorescent display and is powered by three AA size dry cells. These give a useful lifetime of between three and five hours.
• Sinclair Scientific An early scientific calculator by Clive Sinclair. Four arithmetic functions (+ - × ÷) and additionally, log, sin, cos, tan and their inverses. This calculator is dry cell powered and has 9 digit LED display.
• Texas Instruments TI-55-II - (1981). A programmable scientific calculator, with liquid crystal display. This has up to eight user memories (0-7) and up to 56 program steps Program and data memory is shared and every eight program steps take up one user memory, starting at 7 and working back towards 1. Memory location 0 cannot be used for programming. The calculator is powered by two button cells. These retain the contents of memory when the calculator is switched off and last at least a year.
• Texas Instruments SR-51A - (1974). An early scientific calculator with a fourteen digit LED display. This has a built-in rechargeable battery pack, which gives a usable life of about three hours. The calculator has three addressable memories and limited statistical functions, mean, standard deviation, linear regression. I bought this particular example in the early 1970s when it cost about £70.

Front row - some novelties - left to right:

• A credit card sized disposable solar powered calculator - (1999). Six functions (+ - × ÷ % √). This calculator is approximately one eighth of an inch (3mm) thick and has a nine digit liquid crystal display. It is a good illustration of the changes that have taken place since the 1970s, being about the same size and weighing little more than the cover of the battery compartment of the Rockwell 24RD-II described above.
• Casio AQ-2200 - (1982). A six function calculator (+ - × ÷ % √) with additional calendar and timer functions (clock, alarm clock, stop-watch).
• A novelty "book match" calculator - (1989). A calculator disguised as a pack of matches. Open the pack and the keys are printed inside the card cover.

A final word ... Hyper intelligent beings don't need calculators.