charting with a secondary Y axis
 

I am line charting budget data with the following series' Monthly Spend
representing a "spend profile"; Cumulative Monthly spend representing YTD
progress; and Budget representing a target towards which the Cumulative
Monthly is headed. I've added a linear trend line showing where the
Cumulative spend will likely wind up by years end. My problem is I can't
seem to get the secondary axis to show up as a percent of budget. Whatever
the budget number is, I need it to show up at the 100% line on the secondary
axis. Can anyone help?