>>The HP 12c’s reverse Polish notation takes some time to figure out, but you can’t go back once mastered.
RPN >> AOS
Just to post something that will be controversial for some, but it is TRUE!
RPN is the only way. I used an HP 32SII and then an HP-49G. Love it. So many comments are right. Once you use RPN, algebraic calculators are almost impossible to use.
I used to have the Sharp that had 24 characters (PC-1211). Long calculator. Looked cool though. Also had a TI-55 back in the day. Not bad either.