Slide rules are a passion for me, we studied them thoroughly in HS physics before we started the class work in my Jr. year. My 18th birthday gift from my dad was a nice K&E engineers rule, unfortunately it was stolen from my locker. I have 20+ rules in my collection, some were my maternal grandfather's rules, he taught physics and mathematics for the Georgia university system. I was lucky enough to get some rare rules in eBay, with the K&E manuals, a few years back. I understand that a few people are using rules to teach again.

Your 41 was a grail calculator for me when I worked in well engineering, off-shore, never got to get one though. They fetch a hefty price at the auction sites now.

Bill