how to zoom the second scale in (gtk)


I'm currently playing with twinx() and would like to compare graphs, and zoom details.
In demo, it is possible to move the left y scale but not the right one: The sinus stays between -1 and 1.
Is it possible to switch the zoom scale selection?
If I add a button, what should I call?

What if I want to add more y scales, is it possible?