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The Addac adding machine
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The Addac adding machine

The Addac was made by the Addac Company in Grand Rapids, Michigan from 1925 till about 1930. It is a simple adding machine using 8 co-axial number wheels which can be moved using your finger. It has a carry mechanism that works in both directions of rotation so that you can do addition by pulling down the wheel and subtraction by pushing it up with your thumb.

There is a clearing lever on the right with a red button top. These button tops are often missing. The front has a decal that says:

Accurate Adder and Subtractor
To add - pull down
To subtract - push up


Its serial number is 7142 and can be found on the bottom, together with the patent number. The patent was filed in 1926 and granted in 1928, so this one must have been made after that. Earlier ones have "US & FOREIGN PAT. APLD. FOR" on the bottom instead. The largest serial numbers seem to be in the 15000s.

It is constructed using tabs and slots so cannot easily be taken apart.

There are many later co-axial adding machines, but the one that is the most similar is the Solo Handy Adding Machine because its wheels can also move in either direction, whereas most others such as the Addimat only turn in one direction because of their spring-loaded carry mechanism.


Here is a video where I demonstrate the Addac adding machine.

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I have only found one advertisement that has a picture of the Addac, but there are many other small ads looking for agents to sell it. The usual price was about $25. It is not clear when the Addac stopped being made and sold, but the ads seem to dry up in the beginning of 1929. The sterling currency version of the Addac continued to be sold in Australia for a few years after that.

1925-01-10 St Joseph News Press Gazette (Missouri)
1925-04-17 The Morning News (Wilmington Delaware)
1926-03-15 Chicago Tribune (Illinois)
1926-03-31 Spokane Chronicle (Washington)
1926-04-03 Spokane Chronicle (Washington)
1926-05-21 Spokane Chronicle (Washington)
1926-06-12 St Joseph News Press Gazette (Missouri)
1926-06-17 The Des Moines Register (Iowa)
1926-06-26 The Oshkosh Northwestern (Wisconsin)
1926-07-09 Journal and Courier
1926-07-17 Sterling Daily Gazette (Illinois)
1926-07-18 St Louis Post Dispatch (Missouri)
1926-08-08 Sioux City Journal (Iowa)
1926-09 Popular_Mechanics
1927-12-10 The Record (Los Angeles California)
1928-01-11 The Record (Los Angeles California)
1928-04-23 The Morning Call (Allentown Pennsylvania)
1928-06-13 The Sydney Morning Herald (NSW Australia)
1928 Catalog of Copyright Entries
1929-01-31 Oakland Tribune (California)
1929-06-03 The Recorder (San Francisco California)
1929-07-17 The Sydney Morning Herald (NSW Australia)
1929-08-16 The Recorder (San Francisco California)
1930-03-27 Edmonton Journal (Alberta Canada)
1931-01-25 Richmond Times Dispatch (Richmond Virginia)
1933-10-21 The Age (Melbourne Victoria Australia)


The Addac was designed by Andrew Ekman, who was a Swedish immigrant based in Grand Rapids. Aside from the Addac, Andrew Ekman has patents for such things as

He also has several patents for aspects of the Century Adding Machine, an adding-listing machine made by the Accounting Machine Company (known for the AMCO Adding Machine, later called the Star Adding Machine). Note that only his first patent is assigned to AMCO, the rest are assigned to the Bleick Syndicate.

Throughout this time Ekman was based in Grand Rapids, which is also where Fred Doerr, the inventor of the AMCO/Star Adding Machine was based. Another company that was based in Grand Rapids is the Lightning Calculator Company, but it is unclear if there was any direct relationship between all these companies. It is not inconceivable that the Lightning Calculator, the AMCO/Star adding machine, and the Addac made use of the same foundry to supply parts. Other calculator companies were based in Grand Rapids too, such as Barrett, and Add-Index.

PatentFiling datePublish dateNameDescription
US 1,358,42710-12-191909-11-1920Andrew Ekman; Accounting Machine CompanyCarry mechanism
US 1,522,87414-11-192113-01-1925Andrew Ekman; Bleick SyndicateRibbon mechanism
US 1,591,66414-11-192106-07-1926Andrew Ekman; Bleick SyndicateAdding machine
US 1,625,80114-11-192126-04-1927Andrew Ekman; Bleick SyndicateDash pot
US 1,661,60518-03-192606-03-1928Andrew EkmanAddac See also: CA 268,780, GB 248,601.


Rechenmaschinen Illustrated has the Addac with extra pictures.
Rechner Lexikon has a page for the Addac which includes adverts that show the extra legs.
Science Museum Group has an Addac adding machine.
Computer History Museum (CHM) in California has an Addac adding machine.
Museum of Applied Arts & Sciences in Australia has an Addac adding machine.
Chris Staecker's YouTube channel has a great video of the Addac.
The Arithmeum has an Addac adding machine.
ETCetera Online, the Early Typewriter Collectors journal has pictures of the earliest two known Addac machines, with serial numbers 00019 and 00020.

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