Hi Bernie,
What you're looking for can be easy enough, but it depends of course on what you are hoping to accomplish. There's a property node property for an XY graph called Plot Area Bounds, which gives the front panel coordinates for the plot itself (not the entire XY graph, just the plot). You could then reference specific (x,y) point within the graph from a given set of front panel coordinates using a simple math function that subtracts the offset (the xy plot's distance from the top-left of the front panel) from the front panel coordinates and scales it according to the x-y scale in your graph.
An easier way to accomplish all this would be to use a free cursor for the xy graph that the user could move around to the desired position. The Cursor Location property for the active cursor of the graph would then give you x-y coordinates directly in terms of your plot. I'm not sure, however, that that's what you hope to accomplish.
I will attach a VI and a screenshot of an algorithm that do the job with the first method. It's written in LabVIEW 8, so you won't be able to open it in previous versions, but you can look at the screenshot. I will try to save it to a previous version and post it soon.
Hope this helps!
Jarrod S.
National Instruments
