The 1954 machine Hamann 300 (so called version A) – semi automatic ” ratchet” calculator. Machines like this one used coupling angle between rotating shaft and double sided gear to encode numbers being bit faster and less noisy comparing to pin wheel designs.
source.image: A. Dolgicers
This machine uses the same latched wheel construction which all Hamann calculators share as well as the same way an automatic division is performed. The Automat 300 was Hamann’s first calculating machine with a reduced number keypad. In contrast to machines with slide settings or full keyboards, this allows numbers to be entered quickly and blindly.
The predecessor machines, the automats S and T, still have fully automatic multiplication, which was omitted in the automat 300, but due to the laborious entry of the values and the required switching of the calculation type, they are not nearly as powerful, although the arithmetic units in both generations are equally fast work.
A very important feature of the machine for daily practice is the double retransmission. This makes it possible to transfer products from the accumulator or quotients from the setting mechanism directly back into the input mechanism, which enables very efficient chain calculations.