>I've left it out >simply because I have no idea what kind of partial vacuum to expect but for >my own guestimating I've been using -10psi Did you mean negative 10psi? or 10 psi, 0psi would be a perfect vacuum wouldnt it, or did you mean -10 psi from atmospheric so 5 psi? or when talking about vacuums on earth with its atmosphere do we use negatives if under 14.6???