Hi Farrnorth - it's probably best to start a new thread for a new question, rather than add to an existing one - more certain to be noticed on the front page as well :-)
Thanks Lie-in-King. How come it's always you who answer my questions!
I thought someone told me once that I should stay on an old thread but I agree it's much more likely to be noticed on a new one. So I will do so in future.
David
Hi again - I would say that if you've started a thread & received an answer but then find you have another query from the same puzzle, you should add that to your original thread.
If a fair amount of time has passed after the first answer however, a new thread would be fine, IMO.