# Jaap's Mechanical Calculators Page

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.

• It was the first succesful dial adder in which the carry mechanism works in both directions, so subtraction can be performed directly by turning the dials anti-clockwise, the opposite direction from adding.
• The Addometer also has a clearing mechanism, activated by pulling out the tab at the bottom-right corner.
• The stylus can be stored in a hole on the right side, next to the clearing lever, and pulling the clearing lever also ejects the stylus.
• There is a built-in 11-inch ruler along the top of the machine.

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.

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

## History

The Reliable Typewriter & Adding Machine Company seems to have started in the early 1920s, and sold rented and repaired 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 1927 they started selling the Addometer.

The Addometer was invented by Anders Vethe in 1927, and patented in 1928. The Addometer trademark was filed in November 1927, stating that it was in use from the first of that month, and indeed that is approximately when the first adverts for the machine started to appear. It was sold by a subsidiary, the Addometer Sales Company, which had its own store at 184 West Washington Street, a few doors down from Reliable's main store at 170 West Washington Street.

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.

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.

In 1929 the the Reliable Typewriter & Adding Machine Company moved to 303 West Monroe Street, as did the Addometer Company, so they no longer had separate stores. Here they stayed until 1959.

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". At some point the instruction text was moved to above the dials to the right of the logo, and I think this happened in the 1950s. Note that the Dial-a-matic has a very similar instruction text above its dials.

## Models

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.

## Promotional material

Addometer leaflet    (PDF, 1.39 MB or archive.org)
1930s?
4-page folded leaflet
140mm × 225mm

This is an advertising leaflet for the Addometer from the UK. It lists the various models that were available. The leaflet was printed by W.H. Preece & Co in Manchester, which was a company that sold office equipment such as Imperial typewriters as well as office furniture. From at least 1943 until 1958 they were located on Brown street rather than Princess street, so this leaflet was printed before 1943.

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.

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.

Here are various snippets related to the trademarks.

Here are some of the entries in Chicago's Yellow Pages.

## Patents

The Addometer was designed and patented by Anders Eirikson 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