Help with Graph Axis
 

I have a report that I add to weekly, and each new line will be the monday of
that week. Part of the report is a graph that I update, simply by changing
the data the graph uses to include the new row.

So the horizontal axis on the graph is every 7 days (Mondays), but the
problem occurs because I need to have vertical lines on the graph to signify
the beginning of the month.

I've tried setting the axis so a Month is a Major unit, and days a minor,
but it just doesn't work correctly, this means I have to manually draw lines
on the graph, and move them every week. Is there a better way (and more
accurate than my hand) of having vertical lines for the beginning of the
month?