First, as new comer I obviously doubted about this item, the reading help to question oneself not to have the answer. It's why I posted this message even after having looked on books.
Second, sorry if you felt upset by the subject and the post, but the answer to my knowledge is not in the books, although it might help a lot, but in the experience, and so far I thought that you guys had what I missed.
Many thanks to all.
Warm regards.
Chris
ps : Jean, I'm leaving in midi-pyrénées.