Great post! My Dad used his to design electrical equipment for the New York City and other subway systems, the monorails at Seattle and original Disneyland, and rail cars that dumped the cement for the Glen Canyon Dam in AZ. It was literally the last item he removed from his desk when he retired at age 80, though he’d switched to computer long before then.
Your dad had an interesting history. My dad was a Chemical Engineer and I had one of his slide rulers. It was a short one with a suede leather pouch. I ended up giving it to my youngest brother - who is also a Chemical Engineer.