Jaap's Mechanical Calculators Page


Thales KA

My Thales KA
Thales KA Video

Thales calculators were made by the company Thaleswerk, Rechenmaschinen-Spezialwerk GmbH. This company was founded around 1911 by Emil Schubert and was based in Rastatt/Baden in Germany. They made many pinwheel calculators, models A, B, C, D, and M, all with several variations. The design of these pinwheel machines was done by Emil Schubert, but he was forced to leave the company in 1936 due to the rise of Nazi fascism.

In around 1953, Thales came out with a completely different design. This was not a pinwheel calculator, but a simple adding machine of a unique design. It was called the model KA, where KA stands for Klein-Addiermashine, small adding machine. It was produced until around 1963. A version was made for handling British currency which was sold under the name Figaro. There was also an improved model called the KR which allowed for multiplication too, and from 1961 till 1965 they made a listing adder called the model 149. There were variants that were driven by an electric motor, either with the motor bolted onto the back or with it built in.

My Thales KA

The Thales KA has a 9-digit register at the front. It has an 8-column full keyboard on top. The keys are tilted buttons, hinged at the left and sticking up on the right. When you press a button, it is pushed down flat, and it will also force all the buttons of the smaller digits lower down the same column to be pushed in as well. There is a pushbar to the left of the keyboard with which you can reset the keys so that they all stick up again, which is useful for correcting a mistake.

On the right side of the machine is a large lever. Pushing down this lever will cause the entered number to be added to the register. It normally also resets the keyboard so that you can enter the next number to be added.

There is a small switch to the right of the keyboard. Flipping this switch changes the machine to subtraction mode, which means that pushing down the large lever will subtract the entered number from the register. There is another switch at the top right of the machine, the Repeat switch. This controls whether the keyboard is automatically reset after each addition or subtraction. Not resetting allows you to add/subtract the same number several times in quick succession, thereby multiplying it by a small number. It is not possible to do full multiplication because there is no provision for shifting the input or register relative to each other.

The small lever on the left hand side clears the register. Earlier versions of the KA had a clearing wheel at the front right instead. They also had the option of attaching the large lever to the left hand side, and optionally had a 2-digit counter at the back which counted the number of additions/subtractions made.

My Thales KA has serial number 39507 which makes it one of the later ones, probably about 1960-1961. It does however still have a metal case, whereas even later versions used a grey plastic case.

Thales KA
Thales KA
Thales KA, rear
Thales KA, keyboard
Thales KA, switch addition
Thales KA, switch subtraction
Thales KA, logo
Thales KA, clearing lever
Thales KA, underside
Thales KA, serial number

This machine has an unusual mechanism. When the large lever is pushed down, the whole register is moved backwards, passing underneath the keyboard to the back. Releasing the lever returns the register to the front to become visible again. Every key has a small pin attached. Pushing down a key causes its pin to move into the path of the corresponding wheel of the register. If you press for example a 7, then all the keys 1 to 7 in that column are flipped, which puts 7 pins into the path of that register wheel so that 7 will be added to the wheel when it passes underneath. When the register moves forward again it does so a few millimeters further down so that it bypasses the pins. On that return stroke the carries are performed instead by pins that have been flipped up from below.

When the switch for subtraction is set, the whole keyboard is move slightly to the left. This causes the pins of the unpressed keys to lie in the register's path instead. This therefore adds the complement of the entered digits. There are also 9 pins in the column to the left of the keyboard to handle the ninth register wheel, and one extra pin in the first column to make it the tens complement.

When I got my machine, the Repeat switch did not work, and was such that it is always on. The keyboard had to be reset manually every time. It turned out that the machine had been taken apart and reassembled incorrectly. The switch connects via some rods to an axle at the front, and that axle was in an incorrect orientation so that it was unable to engage with the keyboard properly. Simply removing the axle at the rear of the keyboard allowed me to remove the keyboard and then reassemble it correctly.

Thales KA, internals
Thales KA, internals, no repeat
Thales KA, internals, repeat
Thales KA, internals, clearing lever
Thales KA, internals, register
Thales KA, internals, keyboard removed
Thales KA, internals, keyboard unpressed
Thales KA, internals, keyboard all pressed
Thales KA, internals, in action

The instructions are on a small sheet of paper (149mm×210mm).

Thales instructions
Thales instructions
Thales instructions
Thales instructions

It had a one-year guarantee (149mm×207mm).

Thales guarantee
Thales guarantee
Thales guarantee

Thales KA video

Here is a video where I demonstrate my Thales KA.


I have not found the original patent for the Thales KA, only a later one that describes the changes needed for non-decimal calculations such as British currency (sold as Figaro). It mentions the application number of the original patent, but this is crossed out so it may be that the application was unsuccessful.

PatentFiling datePublish dateNameDescription
DE 1,802,903 U25-4-195524-12-1959Thaleswerk G.m.b.H RechenmaschinenfabrikThales KA for non-decimal calculations


Christian Hamann's collection includes the Thales KA, with pictures of its restoration.
Rechenmaschinen-Illustrated lists many Thales machines, including the KA and a KR.
John Wolff has an older model Thales KA.
rechnen-ohne-strom.de has two, the older one with a counter, and a similar one but with a plastic case.

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