Thank you, MIchael.
I tried overlaying the 2 graphs but could not get the y-axis scale to match. I've also tried an alternative way as such:
Add a dummy variable to my data that calculates the difference between the threshold and the stacked data, and plot it as a series stacked on the vary top.
The resulting graph looks like a line over a stacked chart, but it is not clean. I could not change the transparency of the area of this variable so that the area does not show and only the plot line shows. Also, there is an issue when the difference is negative (i.e. the actuals exceeds the threshold).
