Hi Philippe, Apologies for not having replied earlier to you very informative e-mail. I log on less than once a week and so I am often late in my replies. I have over 150 mails still unread... The information you gave looks great, but I am unable to pursue it at the moment, as I am very busy. I hope to start to do this research next month. I find it very difficult to know that I have so much to do and so little time to do it in. I am sure you must find the same. I look forward to following your advice and hope that I am successful. Many thanks again! Penny