David/Peter
Please don't think I am ignoring your message and as you know I'm not usually shy about posting my diatribes here but, with this one, I think Paul was being very kind. If it might be of use though to some I will tidy it up and post it as soon as I can find a little time. Sending it by e-mail was easier and much less likely to wake up the "spelling" police or start a theoretical/practical engineering "discussion".
Best regards
Keith