Ancient times - The abacus is the main aid to calculation.

BC100 - Greek Antikythera Mechanism.

1500 - Leonardo da Vinci conceived the first mechanical calculator.

1600 - "Napier’s bones" invented by John Napier for multiplication, based on the ancient numerical scheme known as the Arabian lattice.

1620 - William Gunter developed a logarithmic rule for multiplication and division using dividers, which was the forerunner of the slide rule.

1622 - William Oughtred invented the circular slide rule, and in 1633 described the rectilinear version.

1642 - Blaise Pascal started to develop a mechanical calculator - the Pascaline. Capable of addition, subtraction was performed by nines-complement addition, and multiplication was performed by repeated additions and subtractions. It had shortcomings and failed to sell.

1673 - Gottfried Leibniz constructed the first calculator capable of multiplication and division. He Developed the Stepped Reckoner using stepped gear wheels. Performed the 4 functions, but worked erratically due to an error in the carry mechanism, none sold.

1820 - Charles Xavier Thomas’s Arithmometer.

1822 - Charles Babbage conceived the original Difference Engine.

1850 - Victor Mayer Amedee Mannheim standardised the modern version of the slide rule.

1853 - The Scheutz Difference Engine completed: the world’s first printing calculator.

1874 - The Odhner calculator, invented by the Swedish engineer W.T. Odhner, is based on the pin-wheel principle. Since then, many calculating machines have used the same principle (eg. Odhner).

1878 - The first direct multiplication machine was built by Ramon de Verea. This is much faster than the shifting carriage or other digital methods.

1884 - Dorr E. Felt invents the Comptometer, the first succesfull key-driven adding and calculating machine. In 1886 he joined with Robert Tarrant to form the Felt & Tarrant Manufacturing Company.

1890 - Calculimetre manufactured by Charpentier.

1891 - William S. Burroughs began commercial manufacture of his printing adding calculator.

1899 - Millionaire calculator introduced. It allowed direct multiplication by any digit - "one turn of the crank for each figure in the multiplier".

1902 - The Dalton adding-listing machine was the first of its type to use only ten keys - first 10-key add-lister.

1947 - Curta miniature hand-held mechanical calculator introduced .

1960 - First electronic desktop calculator - Bell Punch/Sumlock Anita Mk VII - based on cold-cathode vacuum tubes. Orange discharge tube displays used.

1964 - First all-transistor desk calculators - Friden EC130 & EC132, IME 84, Sharp Compet (Prices comparable to that of family cars).

1967 - Four-function Programmable Calculator - Casio AL-1000 (Weight 12.3 kg).

1969 - First calculator using just LSI (Large Scale Integration) chips - Sharp QT-8D , with ICs by Rockwell. Size & weight much reduced, calculator now portable.

1970 - 14 digits with nixie tubes, 4 functions & memory - Facit 1123.

1972 - Bowmar 901B, Made in USA Electronic Calculator.

1972 - First scientific pocket calculator introduced - Hewlet-Packard HP 35. HP Calculator Heritage Page.