[felix318]

I still have my HP 11C, the engineering equivalent, from my school days. It is still a joy to use, the build quality, the feel of the keys, the RPN system. The thing is almost 40 years old and it looks like new.

Sure, it’s totally anachronistic but the heart has reasons which reason knows nothing of.

[Animats]

I still have an HP 11C on my desk. Still running on coin cells from the previous century.

The 12C is used because it can directly calculate present value, which is an integral over an interest rate. That's a non-trivial calculation that everyone who deals with the time value of money needs.

[MegaDeKay]

Same here, only I have a 15C. Still works perfectly. I think I have changed the batteries in it twice since I got it around 1984 despite using it regularly. I swear it is solar powered.