Sorry to interrupt the flow of mathematical/technical exchanges on this forum.
I just wanted to share a thought: when cruising on http://www.hpcalculators.net/HP-67/HP-67%20box1.JPG , I noticed the quality of this HP67 GianMaria found (or maybe it's his own he kept in perfect shape) and especially the leatherette pouch.
It brings back memories of the time I had my very first HP21: I couldn't believe the quality of the pouch, although it came with a low-range calculator. Its softness, smell and much more.
Don't take me wrong: it ain't nothing physical in a politically incorrect way :-)
Just this feeling that you own something special, designed by special people, having the same expectations you have.
This I never forgot and it drove me to always get the top of the cream product if I can afford it. This way I'm sure people did care of me before I have to ask.
Sorry for this long thought but it brought me back in 1974 and I love that...
Good night (midnight over here)