Comptometer
The Comptometer was the first commercially successful key-driven mechanical calculator, patented in the United States by Dorr Felt in 1887.
Consequently, in specialized applications, comptometers remained in use in limited numbers into the early 1990s, but with the exception of museum pieces, they have all now been superseded by electronic calculators and computers.
The comptometer is the direct descendant of the key-driven machine of Thomas Hill[1] patented in the United States in 1857 and of the Pascaline invented by Blaise Pascal in France in 1642.
By just replacing the input wheels of the Pascaline by the columns of keys of Hill's machine, the comptometer was invented.
Dorr Felt began his work on the comptometer in 1882[2] and started building the first prototype during the American Thanksgiving holidays of 1884.
Shortly after, Robert Tarrant, the owner of a Chicago workshop, gave Felt a salary of $6 a week, a bench to work on, and what would add up to $5,000 to build his first practical machine, which he finished in the autumn of 1886.
[6] A Comptograph is a comptometer with a printing mechanism making it more like a key-set calculating machine (even though the keys are registered as they are typed and not when a handle is pulled), therefore slower and more complicated to operate.
It was the first printing-adding machine design to use individualized type impression which made its printed output very legible.
[8] The firm often used the abbreviation Felt & Tarrant Mfg Co in their logo on both their machines as well as in print, with the ampersand chosen over the word "and" as part of their official corporate name.
[10] In 1960,[11] the Bell Punch Company bought the British rights to the Comptometer design and trademark, and continued its development.
Described in patents 762,520 and 762,521, it introduces a new carry mechanism that reduces the power needed to operate the keys to one fourth of its predecessor's.
[12] And finally it introduces a simplified clearing mechanism that only requires one lever, and one back and forth motion of it, to reset the machine.
"The machine gun of the office" as it was called in some World War I advertisements,[13] was starting to develop the form and mechanism that it would keep for the next forty years.
This was a transition machine that introduced the "Controlled-Key" safeguard, which was part of an error detection mechanism that blocked most of the keyboard if a key was not pressed enough to add its total to the result.
Manufactured from 1920 until the beginning of World War II, these models incorporate all of the improvements of the previous machines.
The Comptometer logo is inscribed on their front and back panels and they have the red release key that was introduced with the previous two models.
The ST (SuperTotalizer) has two display output registers and two additional levers that allow for the creation of intermediate results.
The most important new designs of this period came from the Sumlock comptometer Ltd company that introduced the first all-electronic desktop calculators almost two years before the competition.
Sharp's first all transistor desktop calculator, the CS-10A COMPET, introduced in the summer of 1964, also had a Comptometer type keyboard.
