Displaying a graph or a red cross if the graph is missing

I am not sure I fully understand what you are trying to do. If the graph is empty then this is already a good indication that the data is not available, no? But if you want to draw an 'x' inside the graph you could display dummy data like this:

Make/D/O no_data_x ={0,1,nan,0,1}, no_data = {0,1,nan,1,0}
Display no_data vs no_data_x

You could also change the graph background color.  For example, the following sets the graph background color to a light red:

This is a good idea (I think). It requires no new data and clearly shows that the data is missing... I think I will use this approach...

chozo - thanks as well, but I think I will go for this approach in order to not need new waves...

Best,

Johan S

I use the background color in a similar circumstance to yours and it does the job.