Mechanical Calculators

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Addometer

Standard Addometer

Standard 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.

As well as decimal models, versions were also made for working in feet and inches, as above and Sterling currency, as below.

In the standard version the wheels are colour coded for working in currency eg. the two white wheels on the right would be for cents and the rest for dollars, in groups of three. Or the colours can just be ignored and a decimal point inserted mentally as appropriate between the wheels. The addometer above shows the value 87654321, or it could be interpreted as $876,843-21.

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

Feet & Inches Addometer

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.

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.

Sterling Currency Addometer

Sterling currency Addometer.
Sterling currency Addometer.

Sterling currency Addometer.

Details as for the Feet and inches Addometer above.

This version was made for use in countries with Pounds-Shillings-Pence, Sterling currency (see the Sterling Currency Calculator section for more details of Sterling currency).

This requires the fitting of special dials:
The 4 white dials on the left are for Pounds; the two red dials are for Shillings (20 Shillings = 1 Pound); the 2nd dial from the right is for Pennies (12 Pennies = 1 Shilling); the dial on the right is for Farthings (from "fourthings" (4 Farthings = 1 Penny).

The calculator in the photograph displays the value:
£1,234 17s 6 3/4d
(1,234 Pounds, 17 Shillings, and 11 3/4 Pence).

Distributed in the UK. by Taylor's, 74 Chancery Lane, London.

Inside Addometer

Addometer with top cover removed.

This shows the number dials and between them, and slightly above, the plastic gears with strange teeth for transmitting carry overs.
The sliding metal strip at the bottom is for zeroing all the dials. Teeth can be seen sticking up from it.

The Addometer was very popular and together with competitors such as the Lightning Calculator were produced for many years until cheap electronic calculators were available.

Vintage Calculators

© Text & photographs copyright Nigel Tout   2000-2017  except where noted otherwise.