Hi Wim and Piem,
Thanks - I understand it! (BTW Did not know these slicing and edging tools when I started with the dolphin!)
Obviously I am a beginner and will make loads of mistakes. But how do you work? Do you try to figure out these 'problems' when you start a model?
Or is this by trial and error that you learn to start correctly with a model?
Jacqueline

Wish that there was a book on this way of thinking...