The search term you are looking for is likely "Conditional Value List".
Lots of posts and explanations already on here.
Oh thanks i will have a look.
Here are some teaching files that you can explore:
The first has working examples of different conditional value lists. The second has examples that start with ways to enhance the basic value list and then go on to methods for selecting values that go beyond what is possible from a simple value list. Both files have detailed documentation on how they work.
And please note the "geek busking" info on the intro layout.
Oh that's also a nice one.
It's not that hard i see.
I think i can menage it now.
Thanx for the help guys.