Editing Comptometer (section)

==Development==
[[Image:EarlyComptometerKeyboard.png|thumb|left|top|<div align="center">Keyboard of a woody (1895)</div>]]

===Wooden boxes===
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The first machines were built using wooden boxes, which made them lighter but more fragile. They were called the "woodies", and about {{formatnum:6500}} machines were built in between 1887 and 1903.

Two major improvements happened during the first years of production: the first was the insertion of carry inhibit push buttons for quicker operations of subtraction and the second was the color grouping of the columns of keys (three by three except for the first two columns that represent hundredths). Felt continually improved his machine with seven patents filed during the first ten years. These included the patents that he took for the Comptograph.

Each row of keys is differentiated from the one above and the one below by a different tactile feel: the even rows have round and raised keys and the odd rows have flat and oblong keys. The keys of the first machines, with their metal rims, are similar to the typewriters keys of the same period. Plastic keys were also introduced very early on but their rows do not have that tactile difference.

The woodies had a three-part zeroing mechanism: a lever, a lever stop, and a knob. In order to reset the machine, first push the lever toward the stop, start rotating the knob and release the lever as soon as the result numbers start to move. Continue rotating the knob until all the result numbers are reset.

[[Image:Comptometer Model A.jpg|thumb|right|<div align="center">Model A (1905)</div>]]

===Model A===
All the models, from this one on, have a metal casing, but the model A has a polished glass panel for the output display in the front. This model is produced from 1904 to 1906.

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. It also introduces the duplex feature that allows for keys to be pressed simultaneously.<ref>Turck J.A.V., ''Origin of Modern Calculating Machines'', page 149-157, Arno Press, 1972, reprint of 1921</ref> 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,<ref>''The Soldiers' French Phrase Book'', The Felt & Tarrant Mfg Co, advertisement page 54, 1918.</ref> was starting to develop the form and mechanism that it would keep for the next forty years.

===Model B, C, D===
These models are built from 1907 to 1915. They all have the shoebox metal casing that will be used until the end of [[World War II]].

===Model E===
[[Image:Comptometer model E.png|thumb|right|<div align="center">Model E "Controlled-Key" Comptometer with a white release key (1914)</div>]]

Very few machines of this type were built, but all were made between 1913 and 1915. 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. When this mechanism was activated, all the columns of keys were blocked except for the one where the error occurred. Therefore, the operator could find the column in question, reenter the number and unlock the keyboard by pressing the release key in order to resume the operations.

Each key was supported by a metal plate that wrapped around it on three sides. This created a support that was used to block the key when the error detection mechanism was activated. The blocking mechanism was moved inside the box in the following models.

===Model F===
The production of this model started in 1915 and lasted five years. The error detection mechanism is moved inside the box and the release key is red. This machine is the last machine without the Comptometer logo inscribed on its front and back panels.

[[File:2024-04-03, comptometer, model F, 10 columns.png|thumb|Model F, 10 columns, red "controlled key" (1915–1920)]]

===Model H, J, ST===
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.

[[Image:Comptometer.jpg|thumb|left|<div align="center">Model J (1930s)</div>]]

The ST (SuperTotalizer) has two display output registers and two additional levers that allow for the creation of intermediate results. Each key pressed by the operator is added to the top display register creating an intermediate result which is added to the bottom display register when the operator activates the front right lever (it also resets it). The bottom display register accumulates the intermediate results until it is cleared by using the left lever.

These three models are the last of the shoebox design that was introduced in 1907 with the {{nowrap|B model}}.

===Model K===
This electric model was introduced in the middle of the 1930s and had a very moderate success since the mechanical models were very easy to operate and less expensive to maintain.

[[Image:Comptometer Model WM.jpg|thumb|right|<div align="center">Model WM produced during {{nowrap|WW II}}</div>]]

===Model M, WM===
Introduced just before World War II, it had a new box design which was more symmetrical and rounder in shape. The WM was manufactured during World War II with a less wasteful use of material for the mechanism.

The WM had many aluminum parts which were more prone to failure so the use of steel was 
resumed as soon as steel again became available. While the machine was lighter, it was also weaker.

[[Image:AnitaMk8-01.jpg|thumb|left|<div align="center">The ANITA mark VIII sold from 1962 in Britain</div>]]

===Post World War II models===
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The models become lighter with the use of aluminum and more refined inner mechanical designs. Both mechanical and electric models are offered. Their outside is similar to the model M machines. The model 3D11 succeeds to the model M and the electric model 992 succeeds to the model K.
The major external appearance change of the 3D11 and 992, the keys were two tones of green with a fuller depth almost twice the old original style. making identification very easy. Also the lock
release key (red) was moved from the upper right corner of the keyboard to the center and just below the 'one' keys so it could be thumb operated. On model K electrics the motor was turned on with a switch and ran continuously during use. The 992 had a micro switch which started the motor at the start of any key depression and shut off after key action competed. This reduced the motor
wear to almost nil.

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. They were the [[Sumlock ANITA calculator|ANITA Mark VII]], first introduced in 1961 and marketed in [[Continental Europe]] and the ANITA Mark VIII, a slightly improved design, introduced at the same time, marketed in Britain and the rest of the world. They both started shipping in 1962.

The last ANITA machine with a Comptometer keyboard was the ''ANITA mk 10'' introduced in 1965, still using cold-cathode switching tubes and that will be replaced in 1968 by the ''ANITA mk 11'', a 10 key machine.

[[Sharp Corporation|Sharp]]'s first all transistor desktop calculator, the ''CS-10A COMPET'', introduced in the summer of 1964, also had a Comptometer type keyboard.