I haven't used a Curta although my dad did try and teach me. It's kind of like a sliderule - not exactly intuitive. My dad has several Curta's, kind of like the calculators I have kicking around. Don't think I kept the HP45, probably still have a 25c, and a bunch of others. My wife uses an 11c for doing our personal finances. Speaking of the 25c's, they were nearly indestructible. I have to say, the current generation of HP's are built cheap with lousy keypads. Historically HP's have had nice tactile keys that the fingers could dance across ... it's sounds nerdy just writing this. Not so much the recent versions, in fact I'd go so far to say that I "hate" my 35S. The nice keypads are probably why I like my Blackberry (Bold 9900). I won't be switching to a touch screen anytime soon, including the BB Z10.