I’m currently trying to create a line chart showing the refund rate for each customer per item over their sales for the same month so the line chart will have an individual line for each Customer – Item combo.

For example, first line, the refund rate of A – Apple would be calculated by dividing Refunded £ (£6) by the Sales £ from Customer A in that same year_month (May 2024)

I split up the lines by dropping both Customer and Item to the Colour marks card. This works, however, in the colour legend, I would get A, Apple but also G, NULL as it combines all the Sales dataset Customer-Item. If I filter to just keep the ‘Refunds’ Dataset, the table turns blank as there are no sales value to divide by.

Is there some sort of LOD calculations which I fix this?? I’m quite new to Tableau so still trying to get my head round LOD