Non-Decimal Calculators

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Length Calculators

Addometer Mechanical Dial Calculator

Feet & inches Addometer.
Feet & inches Addometer.

Feet & inches Addometer.

296 x 50 x 15 mm (11.75" x 2.0" x 0.6").

Made in U.S.A. 1900s - 1960s.

For addition the stylus is placed in the hole against the appropriate large, inner number and dialed clockwise.
For subtraction the stylus is placed in the hole against the appropriate small outer number and dialed counter-clockwise.
Carry is automatic, and the instrument is cleared by pulling out the tab at bottom right.

Addometers were made in decimal verions, and also for working in feet and inches, as above and Sterling currency.

Imperial Length Measurements In the feet and inches version the wheel second from the right has numbers to 11 for dealing with inches. The wheel on the right deals with eigths and quarters of an inch. The addometer shows the value 123,456 feet 11 5/8 inches.

Made by the Reliable Typewriter and Adding Machine Co., Chicago, Illinois, U.S.A.


Although Britain has largely changed to the metric system of length measurement, the Imperial length system still thrives in the U.S.A. There it is possible to buy electronic pocket calculators which can operate in Imperial length units.

Addometer Electronic Calculator


Addometer, operating in Feet and Inches mode, displaying 10 feet, 8 and 15/16 inches.

Addometer Feet and inches calculator

Display is green vacuum fluorescent.

Has Feet & Inches and Metric modes, and memory.
Metric mode has the standard 4-functions, and memory, while Feet & Inches mode does not have multiplication and division, only addition and subtraction.

3.6v (3x AA rechargeable cells).

Integrated circuit - Rockwell A7872-11 (here date coded 1980).

84 x 154 x 42 mm. (3.3" x 6.1" x 1.7").

About 1980.

Addometer Company, Dolton, Illinois, U.S.A.

The [MET] key changes between Metric and Feet & Inches modes.
The [FT] key defines the number just entered as feet, then the [IN] key defines the number just entered as inches, and the [FRA] key the number just entered as a fraction (rounded to the nearest 1/16th).
In metric mode the calculator operates with a fixed decimal point giving two places of decimals.

This calculator has a case style similar to that of some Rockwell models (see the Rockwell-Anita 201 and 202/SR) and uses a Rockwell integrated circuit. Thus, there appears to be a Rockwell connection in the production of this calculator, however Rockwell had left the calculator market a few years earlier so this connection is unclear.


This calculator was kindly donated by an architectural company and can operate on Feet & Inches for architectural calculations.

Although the Addometer Company, and other manufacturers, had produced mechanical calculators operating in feet & inches for many years, electronic calculators capable of operating in these non-decimal units were late on the scene, and this may have been the first such model.

Nowadays there are several models of electronic calcuators which operate in feet & inches, and also models which use other non-metric units, such as time (hours, minutes, seconds, and frames, useful for television program technicians).

Metric display
Feet & inches display

In metric mode displaying 123456.78.

In feet & inches mode displaying 999 feet, 11 and 11/16 inches (which is a few 1/16 ths below the maximum it can display).


Inside the calculator showing the Rockwell integrated circuit.

On stand

On the rear of the case is a fold down stand, typical of the Rockwell calculators using this case style.

Addiator Addfeet Junior

Addfeet Junior

Stylus Addiator.

The 4 columns on the left are for feet, then the column second from the right is for inches, and the column on the right is for 1/8ths inches.
The calculator pictured on the left and below shows 1,234 feet, 11 7/8 inches.

Designed principally for addition and subtraction.

42 x 160 x 5 mm (1.7" x 6.3" x 0.2").

Made in Germany.

With this calculator is the original sales invoice from when it was bought new. It is dated May 1982, from Midwest Surveyors Service, and it cost $19.95.


This is a very late date for purchasing a new mechanical calculator, but there were few electronic feet & inch calculators available at the time, such as the Addometer above, and they were probably more expensive.

Close up

Close up of the result windows showing  1,234 feet, 11 7/8 inches.

Vintage Calculators

© Text & photographs copyright Nigel Tout   2000-2015 except where noted otherwise.