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The Addometer
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The Addometer

The Addometer is a dial adder. The one shown here is a model B. It has 8 number dials, giving it an 8-digit capacity. Only a small part of each dial is visible. There is a narrow circular slot showing 10 holes around the edge of the dial, and you can enter numbers by putting a stylus into such a hole and turning the dial until the stylus hits the end of the slot. There is also a small window that reveals a digit on part of the dial, and together the 8 windows form the register.


The Addometer was first introduced in 1927, and has several nice features that set it apart from other dial adders of the time.


The carry mechanism is simple but clever. There are intermediate wheels with only 5 teeth. These teeth are splayed so far apart that the adjacent number wheels can mostly turn freely without moving the intermediate wheel. However, if that intermediate wheel turns one step, one of its teeth meshes with the gear under the number wheel to its left and pushes that one step as well. The number wheel to the right has a carry arm that sticks out and pushes the intermediate wheel one step when it rotates from 9 to 0 or vice versa. Each intermediate wheel is at a different height to the next or previous, so that the carry mechanism between one pair of number wheels does not interfere with that of the next.

The clearing mechanism is very cleverly designed. The clearing lever is a toothed rack, and when you pull it out, 9 teeth of this rack will pass each number wheel. The number wheel has a 10-toothed gear with one tooth missing. When the number wheel is on zero, the missing tooth is facing the rack so that the rack can no longer turn the wheel. Conversely, the rack has parts without teeth, so that in its rest position the number wheels can rotate freely without interacting with the rack.
The problem with this system is that there is not enough room between the wheels to fit 9 teeth on the rack. It could have been miniaturised, but that would mean an increase in manufacturing precision, and make it more prone to breaking. So the rack has 4 teeth between the first two wheels, 5 teeth between the next two, and so on, alternating. The lever therefore needs to be pulled out twice as far as the distance between two wheels. To clear the leftmost wheel the rack would normally need to stick out through the left side of the casing, so the left end of the rack has been made collapsable.

Addometer video

Here is a video where I demonstrate my Addometer, and show the mechanism.


The Reliable Typewriter & Adding Machine Company seems to have started in the early 1920s, and sold typewriters and calculators of various brands through a store in Chicago. In adverts the company name was often shortened to Reliable Typewriter Company or Reliable Adding Machine Company, depending on what the ad was for. In about 1924 they started selling the VE-PO-AD (Vest Pocket Adder), a troncet/addiator type of machine, mostly through mail order. In November 1927 they also started selling the Addometer, at first through a subsidiary called the Addometer Sales Company. The Addometer trademark was filed in November 1927, stating that it was in use from the first of that month, and indeed that is when the first adverts for the machine started to appear.

Note that the name Addometer had been used several times before for other, less successful machines (e.g. Jabez Burns' Addometer (1858); Gordon's Addometer (1870s); Prewett Addometer (1916) ), and there was also an Addometer Corporation that was granted several patents for adding-listing machines between 1913 and 1917. It seems however that the word had not been trademarked previously.

Addometer logo

A year after the Addometer came to market, in October 1928, the trademark for the Addometer logo (consisting of the word Addometer with a slightly larger central letter M and ADDO and ETER underlined) was filed. The Addometers made in that first year can be recognised by the absence of the logo, as they just have ADDOMETER written above the first dial in plain capital letters without an underline, and Patents Pending to the right of it. These seem to be very rare.

Most Addometers have the logo above the second dial from the left, and on the front side of the machine are the texts "Reliable Typewriter & Adding Machine Corporation, Made in U.S.A." and "(+) To add - use large figures - turn to right / (-) To subtract - use small figures - turn to left". Some have the instruction text written above the dials to the right of the logo, and I think those were produced much later, possibly in the 1950s.

I do not know how long the store in Chicago existed. It is possible that when the Great Depression hit, the store closed and the company focussed on the Addometer and Ve-Po-Ad.

When the Addometer trademark was renewed in 1949, it was done by J(ames) Arthur Lyons doing business as Reliable Typewriter & Adding Machine Company. It is not clear whether he was the original founder of the company. It seems that he later changed the name of the company, as the last produced Addometers and VE-PO-ADs were sold by Lyons Associates. I do not know when production of the Addometer ended, but it seems to be some time in the 1950s, when cheaper plastic dial adders like the Dial-a-matic and the Kes-Add became available.

In 1969 the trademarks were renewed again, this time by R. B. Zajesky. The Addometers were no longer being made, but presumably he was the man behind the Addometer Company, that was based in Dolton, Illinois, and which made some electronic calculators that had a special mode for calculations involving feet and inches. Those calculators used the original Addometer logo.


The majority of the Addometers are like the one I have (model B), but there were several different models.

A  Last dial is for eighth fractions
B  Standard decimal model, ruler in inches
C  Imperial lengths, 6 dials for feet, 1 for inches, 1 for eighths
D  Equal to B, but ruler in centimetres. Made for export to mainland Europe.
E  Unknown
F  English currency: 4 dials for £, 2 for Shillings, 2 for Pence and Farthings

I have been unable to find out what the model E was. It seems to have had a ruler with centimetres, but it is unclear how it differs from a model D.

The model designation is usually stamped or printed on the left side of the machine. Apparently the oldest Addometers have a serial number on the underside, and sometimes there was a handwritten serial number on the inside.

Advertisements and articles

Below are some of the advertisements that I have found for the Addometer or by the Reliable Typewriter and Adding Machine Company.

1922-04 The Business Educator
1922-10 Business Educator
1923-11 Typewriter Topics
1924 The American Digest Of Business Machines
1927-10 Popular Mechanics
1927-10 The American Legion Monthly
1927-12 Popular Mechanics
1929-08-16 De Sumatra post
1929-11 The American Legion Monthly
1940-07 The Carpenter
1947-04-22 Algemeen Indisch dagblad
1947-05-12 Nieuwe courant
1948-01 Popular Mechanics
1948-04 Plastics 1
1948-04 Plastics 2
1948-10-07 Suttons Bay Courier
1950-11-13 Newsweek

The following ads are all for the Ve-Po-Ad adder. Note that when the Addometer was released, the addressee changed from the name of the company to C.M. Cleary, who was apparently the sales manager.

1924-12 Popular Mechanics
1925 The World almanac and book of facts
1926-09 Popular Mechanics
1927-04-04 Business Womens Herald
1927-05-30 Business Womens Herald
1927-06 The American Legion Monthly
1927-08 Weird Tales
1927-09 The American Legion Monthly
1927-11 Amazing Stories
1927-12-05 Business Womens Herald
1928-06 The American Legion Monthly
1928-07 The American Legion Monthly
1928-10 The American Legion Monthly
1928-11 The American Legion Monthly
1928-12 The American Legion Monthly
1928-12 The Goblin
1928-12 True Detective Mysteries
1929-04 Ghost Stories
1929-09 The American Legion Monthly
1929-10 The American Legion Monthly
1929-11 Popular Science
1929-12 True Detective Mysteries
1930-01 Popular Mechanics
1937-01 Popular Mechanics
1938-02 The American Legion Monthly
1939-11 Popular Mechanics
1939-12 The American Legion Monthly

Here is a judgement from the Federal Trade Commission in 1937, in which the Reliable Typewriter and Adding Machine Company was found to be lying in its ads for the Ve-Po-Ad.

1937-11 Federal Trade Commision 1
1937-11 Federal Trade Commision 2
1937-11 Federal Trade Commision 3
1937-11 Federal Trade Commision 4
1937-11 Federal Trade Commision 5
1937-11 Federal Trade Commision 6
1937-11 Federal Trade Commision 7
1937-11 Federal Trade Commision 8
1937-11 Federal Trade Commision 9

Here are various snippets related to the trademarks.

1948 Official Gazette of the United States Patent Office
1948 Official Gazette of the United States Patent Office2
1948-02-17 Official gazette of the United States Patent Office
1948-03-02 Official gazette of the United States Patent Office
1949-04-05 Official Gazette of the United States Patent Office
1968-11-19 Official gazette of the United States Patent Office
1969-01-07 Official gazette of the United States Patent Office


The Addometer was designed and patented by Anders Vethe. In 1926 he patented another calculator, with parallel number wheels that you could turn with your fingers. It used a 5-toothed intermediate wheel, similar to what he then used in the Addometer's carry mechanism. In 1926 he was based in Oslo, in 1928 in Chicago, and in 1932 he lived in Paris where he worked for the Bull Company (US 1,971,860). It is unclear whether he was involved in the commercial exploitation of the Addometer.

PatentFiling datePriority dateNameDescription
US 1,829,37920-10-192627-10-1931Anders E. VetheAdding machine
See also DE 482,656 C,
US 1,764,91510-09-192817-06-1930Anders E. VetheAddometer
See also CA 293,722, CH 132,959.


Rechnerlexikon has a page for the Addometer.
Rechenmaschinen-Illustrated has a little info about the Addometer.
Rechnen Ohne Strom shows an Addometer
Rechnen Ohne Strom shows an Addometer and has a page about carry mechanisms.
Vintage Calculators has an Addometer page.
John Wolff has various dial adders including an Addometer.
The Slide Rule Museum has a page of adders which includes an Addometer.
Hamann has a standard metric Addometer B as well as a fractional Addometer A.
The Computer Collector has a multi-lingual instruction sheet for the Addometer.

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