Could you please provide the sample workbook so i will try.
How do you want to calculate the percentage of sales?
Ideally it should be
a) Percentage sales of Product A should be percentage of Total sale value.
but your attached image shows otherwise
b) It has product with highest sale value=100% and other product sales are calculated w.r.to product with highest sale.
For above solution "a" follow steps:
1: Drag Sales twice in rows deck
2: Right click on second SUM(Sales)
3: Apply Quick table calc> Percentage of Total
4: Apply Dual axis
Please let me know, if this solution helps or you intend to achieve something else.
This is quite simple and you do not need dual axis unless you need to show these
Create a basic line graph with sales.
Drag Sum(Sales) to the Label Box.
Add Table Calculation and change to Percent of Total.
Drag Sum(Sales) to label box again
Click on label You will now be able to format both the percentage and value to appear in the format you require
If you have any difficulty or need me to create this with superstore data then please let me know.