Hi Marc, it is possible to make construction lines that stick around longer than just the current command.

See the CLine command in these previous posts:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1029.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=1029.25

If you install that plug-in, that will give you a new ConstructionLine command, and when you run it (set up a shortcut key to launch it), it will let you drag out several construction lines which will won't disappear automatically. They don't get saved into the file though so they will last until you open another file.

In the future I want to make it possible to save construction lines into files as well, but it probably needs some kind of additional interface to allow for selecting them since normally they try to stay out of the way of selection type actions.

There are also a couple other cline related scripts here:
http://kyticka.webzdarma.cz/3d/moi/#KeepCLine

There's one there that you can put on a shortcut key and when triggered it will make any construction lines that you created in the current command to remain until the end of that file session.

- Michael