How do I add an extra x-axis to an existing graph?

Question

I am trying to produce a graph that looks similar to this, with a certain series against a flow (Q), with an added return interval (T). In the example below the "series" is the reduced variate.

When searching online all I find is adding an extra plot line however this isn't what I'm after.

Thank you very much!

Answer 1

You can not do that directly in excel, but you can get a similar look by using another series and formatting it to look like an axis

find below a screenshot of a similar example.