Parts of the text is extracted from the John Wolff website.
Content without guarantee! (UK); Inhalt Ohne Gewähr! (DL)

Type name / number: Adding Machine: Contex X-10
Part of a 10 key series; X-10, X-20, X-30, X-55
The X-10 is manual driven by handle. The basic machine of a series of four,
Unlike other ten key machines this series has the display in front and the key's at the back side .
Production / SN: 434 056 392
Calculating principle: Rocking Segment
Calculating functions: Add, Subtract, Multiply , Divide (last two by repeat adding / subtracting and shifting of the result register)
Input accuracy 10 digits
Calculating accuracy: 11 digits
Extra's: In the display window: total / result register and a single digit counter register. The last has two sets of figures in nine complements in red and normal in black, for divide and multiply.
Multiplier digits are entered from the least significant digit on.(ie, right to left) in the usual manner for a current calculator, but obvious when you know that the units come first then the pin box is shifted followed by the ten etc. Please see : "How do they calculate", Rocking segment, page 5.
Short form user instructions on the bottom plate.
Designer:  
Production year: between 1957 until ??
Case material: Polyurethane and the bottom plate aluminum.
Weight: 2.67kg
External links: help for repair: http://www.csparks.com/contex/
Previous owner: N. Baaijens, Lochem, The Netherlands
(The first one of the Baaijens collection which is add to the site.)
Cosmetic imperfections:
(I accuse no one)
The plastic feet's are broken in time. I turns out that this material was not suitable for this purpose. Older machines have problems with rubber but some twice as old are in better shape.
Date of receiving: 2012-10-08
Machine story:
2012-10-10
Fully functional on arrival. Cleaned and photo's made of this ingenious machine.
The synthetic materials (polyurethane and nylon), used for the feet's, are very advanced for those times. But it turned out to be unstable in the current machines. These materials are used in the critical areas as well and make the machines some times unstable unreliable. So far this one is not affected yet.