Non-decimal electronic calculators were highly unusual in the days when displays only had 8-digits.
Below are two feet & inches electronic calculators:
Addometer Feet and inches calculator
Distinctive features: Feet and inches calculator.
Technical details:
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.
Inside the calculator showing the Rockwell integrated circuit.
SCAT THE DIMENSION - FEET & INCH CALCULATOR (FI-21)
Two versions with the same functionality.
Distinctive features: Feet and inches calculator.
Technical details:
Display is 8 digits, red LED.
Has Feet & Inches and Decimal modes.
9v (PP3 battery).
84 x 154 x 42 mm. (3.3" x 6.1" x 1.7").
About 1980.
Manufactured by South Carolina Applied Technology, U.S.A.
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).
Text & photographs copyright, except where stated otherwise, © Nigel Tout 2000-2025.
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