How to create a average line of many lines in a line chart

[Anonymous]

Hi guys,

I hope you're doing well !

I would like to add to this graph an another line which will represent the average of all others line and this by Year-Month

To do this, I have used the feature Average line in the "Add further analyses to your visual" subtab in the Visualiazaitions

but it just gives me a lineaire line = 148.43 so it doesn't depend on the axis Year-Month. Please could you help to find a solution or improve this one ?

Thanks