Solved Excel 365 - line graph problem

I have 3 columns of data:
Col.1 Dates in descending chronological order (most recent at top)
Col.2 mpg associated with each date
Col.3 £/litre associated with each date

I want the line graph to show this data with the dates on the X-axis showing the most recent on the left. Seems perfectly reasonable.

When I create the graph I set mpg values on the primary Y-axis, £/litre values on the secondary Y-axis. I also set Format axis (X-axis) to have Dates in reverse order thus giving the most recent on the left.

mpg data is correctly plotted with the data reversed to match the dates on the X-axis, i.e. newest on the left; but £/litre data is not reversed and has the oldest data on the left.

I've tried all sorts of things.
- Reversing the Y-axis just inverts the data vertically.
- Plotting with just one data set and adding the second afterwards gives the same wrong result

It always seems to be the £/litre data set that is plotted incorrectly, even if I initially create the graph with only Dates & £/litre data then add mpg data.

I feel it may well be something to do with the 2 sets of data and their respective Y-axes.

I'm clearly doing something wrong but cannot see what.

Any thoughts?

Solved it. It's due to Excel adding a second horizontal axis when a second data set is added and this doesn't take on the Reverse property of the first horizontal axis. This axis is hidden. So had to make it visible, set it to Reverse, then hide it.