TheThe R44SM is the final evolution of the Mercedes-Euklid calculating machines, whose long history includes the world's first fully automatic calculating machine, the Model 7. This model is based on the Mercedes-Euklid Model 38MS, which was first introduced in the 1930's. After the war, the name was changed to simply “Mercedes”, and then finally to “Cellatron” in 1964. Despite all the name changes, the underlying proportional lever mechanism has remained the same, and is unique to this manufacturer.

The most notable feature of this machine is the impressive 20-column full keyboard. There are two methods for performing multiplication on this machine. The first method enters the multiplicand and the multiplier side-by-side, each using ten columns of the keyboard. When the multiplication button is pressed, the product appears in the results register on the carriage. The other method allows the entire keyboard to be used for the multiplier, up to twenty digits. A button is pressed, storing the multiplier in a non-visible control register, and then multiplicand can be entered. The product is limited to the twenty digits in the results register in either case.

Another feature unique to this manufacturer is the ability to display negative results directly, not as their tens-compliments as with most rotary calculators. The number wheels on the results register have a dual set of numbers. A small lever on the carriage moves a shutter to reveal each set of numbers individually.