According to the position of the control knob socket 1, 2, 3 or 4 is connected to the common socket C.

As the module is fully passive it works bidirectional, i.e. the sockets 1...4 can be inputs and then C is the output. The other way round C can be the input and the sockets 1...4 are the outputs.

By means of an internal jumper the terminals C of both switches can be connected. That way the module can be used as kind of a miniature 4x4 matrix. Rotary switch A is e.g. used to select one of the four sockets 1...4 as input and this signal is sent to one of the four sockets 1...4 of switch B. 

Applications:

switching of audio or control signals in the modular system without the need to unplug and plug patch cables (i.e. no signal interruptions)
building a small 4x4 miniature switch matrix