K4 A is the factory designation, most folks refer to it as the Automat MX. Could also be referred to as the "Automat II" or "3.5 A".
Like Dan said, the knob just indicates frame numbers if you've installed the Rolleikin 35mm film adapter, but doesn't affect 120 film use if the rest of the kit is not installed.
If you're looking for a manual
Butkus Camera Manuals is a good source (for a small donation). I don't see the MX manual in his list, but the manual for the Automat X should suffice. The only differences between the two cameras is the M-X selector switch for flash, some internal light baffles and a change in design of the tripod socket.