How to use the common axis?
The common axis represents a list of signals with the same Y-scaling. It is just a grouping of single signals to one axis.
A common axis can also be created when another signal is added to an already inserted signal in the Graphic window by drag & drop. Doing so the signal needs to be taken to the extreme right of the legend. Here an area appears where the signal is "dropped".
If the signal is inserted, the area is highlighted. A double click in this area opens the configuration dialog for the common axis.