How To Change Simple Graph Using VBA Coding

I have never coded for graphs using VBA where when I run the macro it changes to the 20 most recent data values collected. If column "A" is going to house my y-values and column "N" is going to house my x-values, what would be the coding to change the graphs data range?

My Idea: I am thinking to get the 20 most recent values I could use a row variable that would equal

Code:
Cells(Rows.Count, "A").End(xlUp).Row

This would find the last data point entered. I just don't know the proper syntax to manipulate a graph.