Hello Lukas,
There is an
example available here that demonstrates how to draw a circle on a picture control using the mouse cursor.
If you add a graph to this example, and make the picture control's background transparent, you will be able to draw circles on the graph display using the mouse cursor.
In the future, if you create a new post instead of replying to an existing thread you will have a wider exposure to all of the LabVIEW developers on the forum.
Scott Y
NI