Hmmm.
I am going to guess here because I only once measured in the tube and that was a long time ago. I have been seeing, under vacuum, about a half inch more than I am when normally erect. I know this approximately because I have made lines on my cylinder to mark progress.
If I ever get to the top of my tube (10”), I may challenge Bib to a dick dual. Under vacuum, I can usually hit 9, but 9 has never cemented for me. Maybe because I have such a casual attitude about my own PE routines now.
Flaccid stretch: it’s about the same difference. I can stretch on a good day a half inch more than my normal erect length. Sometimes just a third of an inch. I don’t know what that means. Do you?