I keep one in my office, and use it occasionally too. I get some funny looks from some of the other engineers, but sometimes it is faster than a calculator and gives me all of the precision I need.
I think I have one, too. I've had it for years, but I don't know when I got it, and I have no idea how to use it. My husband is a systems analyst, and I think even he saw it and asked, "What is this thing?" :-)