Secondary Axis in a Pivot-Chart does not stay
 

Hey everyone.
I have a pivot-chart and I need one of the lines in the graph to be in a
secondary axis, as the values are much greater than the ones from other
products. I can do it once, but every time I filter something else, it goes
back to the initial configuration (1 axis only). Is there a way to "fix" the
secondary axis in a pivot-chart even when I change any of the fields to what
I need to see?
Thanks.
Saddy