Bowmar MX-50 (90505)

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The smaller version of the first American-made pocket calculator, the Bowmar 905 was available from 1972. After disputes between Bowmar and the manufacturer of the chip (Texas Instruments) turned to legal action and prices in the pocket calculator market continued to fall, Bowmar also sought to source parts from other companies and to produce them in-house. The MX-50 (model numbers 90506 (USA, black), 90515 (Canada, black), 90516 (USA, beige), and their successor 90505, appeared in the same housing as the 905, contained Rockwell chips that was capable for percentage calculations compared to their predecessor. Over time, the design has changed several times: instead of the beige color inherited from the 905, it has been given a black housing, and then the keys have been replaced with ones used in other pocket-sized models. Due to insufficient manufacturing capacity, the display often came from third-party manufacturers, but most of the keyboards were replaced with in-house ones from 1974 onwards. Later, the MX-50 was replaced by the MX-55, which used algebraic logic.

Small amounts of the MX50 was made in cooperation of Híradástechnika Szövetkezet, Hungary (Telecommunication Cooperative) in 1973-74; its type designation was K-831.

The interesting thing about these calculators is the mixture of algebraic and arithmetic logic: multiplication and division are calculated with the = key, but addition and subtraction are still done by pressing the + and - keys after the second operand. This means that the calculation of (3 - 2) × 4 + 6 is as follows: 3 + 2 - × 4 = 6 +.