Mechanical Calculators

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Madas 20BZS

Madas 20BZG

Madas 20BZS

Mechanical, electrically driven, stepped-gear calculator.

4 functions - addition, subtraction, multiplication, division.

The accumulator is at the top and can show a result to 20 places of decimals. The numbers entered can be to 10 places of decimals.

375 mm x 320 mm x 215 mm (15" x 13" x 9"), 16 Kg (35 lbs).

Made in Switzerland by H.W. Egli S.A., Zurich.

Dates from 1950s or '60s.

Underneath Madas

View underneath, with the bottom cover removed, showing the electric motor which powers this model. Hand-operated models were also available.

The name "Madas" is derived from the initial letters of "Multiplication, Automatic Division, Addition, & Subtraction". It is a mechanical calculator, driven by an electric motor and automatically performs the four standard functions (with a lot of whirring and clunking !).

These machines evolved over many years from the "Millionaire" calculator.


The history and internal workings of Madas calculators are described in an excellent article by Ray Mackay at

In John Wolf's Web Museum there is an overview of Millionaire and Madas calculators, including some incredible pages showing a similar Madas calculator disassembled into its various mechanisms. It vividly illustrates the vast number of high-precision components required and the ingenuity in squeezing everything into a small space.

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