c1427 said:

Our usage scenario for annotations:

1. XamDatachart is displayed to user|
2. User right clicks on chart and selects context menu command to 'Add Annotation'
3. An editable text box is added to the chart at the right click location (upper left hand corner of text box matches the right click location)
4. User enters text into the annotation edit box
5. User hits return or the textbox loses focus (annotation is created)
6. User hits escape or hits return with an empty annotation (annotation is deleted/not created)

Extra scenarios:
7. Create an annotation in C# code
8. Loop through annottaions in a chart and get XY location, style, text, etc.
9. Determine, given an XY location on the control if the location has an annotation at the XY location (i.e., we capture the right click to let a user edit an annotation a second time or delete the annotation)
10. Let a user click and drag an annotation.

I have made exactly that. I started out with this link.... let me know if you need more help, maybe I can assist you.

I too have implemented something similar (lots of different types of annotation, some related to series data, some simply painted over the chart) but my adventure started here, which explains the positional logic required in response to user interaction: