Thank you Tushar,

Your links helped me to see that I can input the line as a second
series and I can manipulate that through the source data to solve
part of the problem, however, I would still like to manipulate
the line with the arrow keys. We have a very old DOS based
program that does this part of the procedure very well, unfortunately
that is about the only thing that it does do well, the rest is frustratingly
painful.

Any other ideas?

Regards
Martin