Retrotechtacular: Mechanical Arithmetic For The Masses

Last month we carried a piece looking at the development of the 8-bit home computer market through the lens of the British catalogue retailer Argos and their perennial catalogue of dreams. As an aside, we mentioned that the earliest edition from 1975 contained some of the last mechanical calculators on the market, alongside a few early electronic models. This month it’s worth returning to those devices, because though they are largely forgotten now, they were part of the scenery and clutter of a typical office for most of the century.

The Summa's internals, showing the register on the right and the type wheels on the left.
The Summa’s internals, showing the register on the right and the type wheels on the left.

Somewhere in storage I have one of the models featured in the catalogue, an Olivetti Summa Prima. I happened upon it in a dumpster as a teenager looking for broken TVs to scavenge for parts, cut down a pair of typewriter ribbon reels to fit it, and after playing with it for a while added it to my store of random tech ephemera. It’s a compact and stylish desktop unit from about 1970, on its front is a numerical keypad, top is a printer with a holder for a roll of receipt paper and a typewriter-style rubber roller, while on its side is a spring-loaded handle from which it derives its power. It can do simple addition and subtraction in the old British currency units, and operating it is a simple case of punching in a number, pulling the handle, and watching the result spool out on the paper tape. Its register appears to be a set of rotors advanced or retarded by the handle for either addition or subtraction, and its printing is achieved by a set of print bars sliding up to line the correct number with the inked ribbon. For me in 1987 with my LCD Casio Scientific it was an entertaining mechanical curiosity, but for its operators twenty years earlier it must have represented a significant time saving.

The history of mechanical calculators goes back over several hundred years to Blaise Pascal in the 17th century, and over that time they evolved through a series of inventions into surprisingly sophisticated machines that were capable of handling financial complications surprisingly quickly. The Summa was one of the last machines available in great numbers, and even as it was brought to market in the 1960s its manufacturer was also producing one of the first desktop-sized computers. Its price in that 1975 Argos catalogue is hardly cheap but around the same as an electronic equivalent, itself a minor miracle given how many parts it contains and how complex it must have been to manufacture.

We’ve put two Summa Prima videos below the break. T.the first is a contemporary advert for the machine, and the second is a modern introduction to the machine partially narrated by a Brazilian robot, so consider translated subtitles. In that second video you can see something of its internals as the bare mechanism is cranked over for the camera and some of the mechanical complexity of the device becomes very obvious. It might seem odd to pull a obsolete piece of office machinery from a dumpster and hang onto it for three decades, but I’m very glad indeed that a 1980s teenage me did so. You’re probably unlikely to stumble upon one in 2019, but should you do so it’s a device that’s very much worth adding to your collection.

Header image: ElioAngelo at Italian Wikipedia [CC BY-SA 4.0].

23 thoughts on “Retrotechtacular: Mechanical Arithmetic For The Masses

  1. Oh my. I have just gone down the rabbit hole of time, I worked on both the machines mentioned in the text and many others made by Olivetti an Italian company. I went on to make my living in Electronics, Hardware and Real-time Software. Designing many different things using the base knowledge I learnt from simple office machines including Typewriters, Adding Machines and early computers.
    Although they seem complex they taught you that if you broke the process down far enough it became a set of simple steps and that is something that stood me very well through my hole career. I’m retired now but I still potter as a bit of a maker with hands that shake too much but the old brain still churns out the software without too much trouble.
    The early computers were really electronic versions of the big accountancy machines that stored the current state as print on big cards with a magnetic strip down one side. A backup, if one existed, was a second physical copy of the card because there was no long term memory, and but did those cards take a pounding.
    I think I have lived through one of the most exciting periods of history, being born just after the first transistor was made and living to beyond the point where we all have computers in our pocket.
    I still love every minute of it!
    Happy Days

    1. I have that feeling too, I feel lucky to be of the first generation who received 8-bit home computers as a young teenager.

      The Summa fascinated me as a spotty teen. I didn’t dare dismantle it, but I spent a lot of time working out how it operated.

    1. Nope. that would be the Anita electronic calculator, using the same architecture as the mechanical ones, but build with tubes, decatron and nixies. the programma 101 used a mechanical serial memory and interleaved cordwood pcb design. we have both in our collection at hack42, but both not working. :-( the Programma 101 needs 974 new contacts for the backplane board and the Anita is unrestored

          1. Hi, I am now in contact with Gastone Garziera, to see if they are still available for a repair or know who else from the association is available for doing that. I’ll let you know how evolve the situation.

  2. Jenny, you DID see our friden mechanical calculator topped off with a solenoid on each button at hack42 did you. next time you come, i can tell you something about it. It used to be of a Friden accounting machine, using a converted and rebranded IBM model C typewriter, bolted to a office desk with this mechanical calculator in the cupboard, and a huge board with stepper relays and other relais (missing..) to do accounting. Using a mechanical calculator in a electromechanic calculating desk. we have the documents for this beast but only the calculator and typewriter remain.

        1. I wouldn’t claim that as a victory of the currency. If it were the older generation would be baffled by the decimal arithmetic anyone born and raised since 1970 can do. The teenage cashiers who can’t count out change in coins seem to disprove that idea.

    1. During the 1970s, after pounds, shillings and pence were abolished, my father used one of these Olivetti calculators (a slightly better model, with an electric motor), for exactly this reason. He was writing a book about mediaeval accounts and needed to do £/s/d arithmetic. If anyone wants to look it up, the (largely uninteresting to outsiders) results were published as “The Tax Book of the Cistercian Order”.

  3. My grandfather, who did the accounting for the small-medium sized company he’d started, had a monster motorized mechanical calculator that allowed you to enter, as I recall, 8 digits, and then add/subtract/multiply/divide that by another 8 digit number. It only had a single carry digit, so you could rapidly get carry faults. But what I most liked about it, that he eventually asked me not to do anymore, was dividing a number by 7, because it would chug away at the repeating decimal for so long it would start smoking. It was an amazing machine, and I was sorry when it broke and he replaced it with an electronic calculator.

  4. LOL ! I have really forgotten about these machine. I worked in an office in 70’s where we had several of them. We also had a different one that didnt print but rather showed the results on the numeric tumblers.. The operation was through spinning a crank lever on the side, forward and backwards with keys to shift results left-right (Facit brand if I correctly remember).
    No one could figure how to make division using that thing and it was left to the side. I proudly came up with the “how to divide” after some fidgeting with it.
    Soon enough I bought my first Sharp Electronic calculator with green mini-nixie tube digits that could extract square roots and perform floating point operations, wow !
    But the rest is history. Thanks for the memory poke.

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