Hope you are well, In the properties of your chart there is a tab labeled Axes. In this tab will be a box labeled the "Expression Axes" (similar to a Y Axis) and here you can select which Expressions you want to have on the Axes and which you don't by selecting the expression and checking or unchecking the box labeled "Hide Axis".
In the same "Axes" tab you can also specify which side of the chart you want the expression axis on in a box labeled "Position" where you can select if you want the select axis on positioned on the Left (bottom) or Right (top).
You will probably want to hide all the axes' that you don't want to show, but that should allow you to have to unrelated line's on two seperate axes.
I have tried that and it did work...
I guess the mayor issue here is that QlikView is not displaying graphically the expressions I have created.
1 - RangeAvg(Before(SUM([STH $]),0,13))
2 - Sum ([INV $])/RangeAvg(Before(SUM([STH $]),0,13))
Even QlikView performs the calculation, it looks like it does not understand how to put it into the graphic.