Bowmar MX75

Bowmar MX75
Bowmar MX75


The Bowmar MX75, which was made in 1974 is an ambivalent device: On the one hand, it has got a vintage looking soapbox-like case and is internally constructed in an old-fashioned way, otherweise it already offers state-of-the-art calculation power with the four basic arithmetic operations, standard entry logics and accumulating memory.


For a pocket calculator of 1974, it is inconvinient, that the large double-sided boards looks like manually designed and populated and even five ICs were used. There's at first the CPU, a Rockwell A1030PE, made in may 1974, two ICs DM8895N and two ICs, maybe display driver, DM75494N, all made in april 1974.
Furthermore, a lot of diodes, resistors, transistors, a handful of tantal capacitors and even a coil were soldered - such a opulent assembly was no longer usual in 1974.

back side
back side

The design is classical, almost vintage: With a maximum height of 3.7cm and a size of approx. 12 x 8cm, the calculator indeed looks like a soapbox and is certainly too big for a shirt pocket. A large part of responsibility for the height has go the large PCB, which fills the case in full size, then the three AA cells below, which shall guarantee five hours of continuous operation, and the angled LED display, which has rather large numbers because of its large magnifying glass.
Not much responsibility on the height has got the Klixon keyboard, with is connected by a nine pin socket and is extremely pleasantly to use. Hardly any other keyboard can compete with a Klixon keyboard: The pressure point is excact and accompanied by a click, and it can be quicky used without bouncing. Unfortunately since this type of keyboard was expensive, these keyboards were not often used.

inside and batteries
inside and batteries

The MX75 offers the four standard calculation functions, which were useual these days. It has also got an adding memory function, which can be enabled and disabled by a switch below the display and read and deleted by two keys. If the MX75 is in calculator mode, on the display there's a slash visible:

display in memory mode
display in memory mode

Empty batteries lead to a "L" at the first position; Division by zero and overflow are indicated with a "C" on the left:

display on errors and overflow
display on errors and overflow

Technical data
CPURockwell A1030PE
Display8+1 digit LED
Number of keys 20
Entry logic (classificationALG (BCBA)
1 + 0.000 = 1.000 (the correct value would be 1.)
0 / 0 = Error
Power supply 3xAA (internal)
Size12 x 8 x 3.7cm
Serial Number147767
Original PriceDM 398.--

Bowmar calculators (en) (Many other Bowmar calculators from the Buffalocalcs collection)
Bowmar MX55 (en) (One of the predecessors of the MX75)
Datamath Calculator Museum: The Klixon Keyboard (en) (Very extensive description of the Klixon Keyboard)
Pioneering Calculator Companies Pioneering Calculator Companies: Bowmar (en) (Article about the history and calculators of Bowmar)
The TI Klixon Keyboard (en) (An article by Guy Ball from the magazine "The International Calculator Connector")