It's really useful having a someone like Bill on hand to sort out these probs (he has fixed it for me too

) - I just hope he never gets 'rationalised' out.
An engineer's answer to fault finding...
If I told you to think of a number between 1 and 100 and then tell me if my guesses were too high or too low, I would start at 50 then go to 25 or 75 etc. That way I would need, at most, seven guesses. If I had started at 1 and just worked upwards I might need 100 guesses. The first technique is called a binary chop and it can also be used for fault finding. First try to establish the possible range for the fault then try to divide that range in two and prove which half it lies in. Repeat until you have located the fault. The skill is in knowing the possible range of faults (which is where Bill comes in) and making correct assumptions from what you have observed (Bill again) - it's all too easy to convince yourself of something and make a wrong assumption. If things don't add up then go back a few steps and try to re-evaluate what you've proved.