I don't work much with dialog boxes, especially for the type of tweak you're asking for. I'm certain it would make my script better if I added your feature, but I lack the time to learn more on this matter.

Does the script work properly, in general? All you have to do is to move the two objects you want compared to the top of the list. It's the best workaround I have to offer.

If you wish to learn how to script, here's a cool resource for learning Python : http://www.codecademy.com/tracks/python
Also, for scripting in Graph, you'd have to take a look at the menu "Help>>Scripting Engine Documentation".
The best thing then is to have a look at pre-existing Graph scripts.

I'm sorry I can't help more...

Start a new Graph instance.

Enjoy.

GraphUser3546

P.S.: I have taken the liberty to add some intelligence to the plugin. It can only be executed when you have at least 1 pt series and 1 standard function. The plugin will check the distance between only the first pt series it encounters and the first function it encounters in the left-hand list. Should work well. I haven't tested it thoroughly, but it does the calculation correctly. Post here if there's anything.

But first, here's what I think I would do, tell me if that's how you'd like it :

- In a Graph file, you'd need to have only, and in that order, the Axes, the Point Series and the Trend-line Function.
- You'd then select the Plugins menu and click on "Calculate Trendline Distance"
- This would create a new Point Series which would hold the distance between the original Point Series and the Trend-line Function, for each point in the original Point Series.

As a matter of sign convention, when the trendline is below the point, would you like the Distance to be a positive number?