Hi, all;

cannot agree with the focussed affirmative: "ordinary people could not work straightaway with RPN". Instead, I support d.b.'s always clever analysis (Hi, D.B.).

I'd add that almost 22 years later, the HP12C still keeps its place at financial markets, and there are not so many engineers there, instead many mathematicians and lots of businessmen, MBA's, market analysts... They are far from being "ordinary people", of course, but their main concerns are far from being the operation of a particular calculator and its operating system. And I'd guess their HP12C's do not have wearied out [n], [i], [PV], [PMT] and [FV] plus digit-input keys only, instead [ENTER] is included. And HP12C users know it well: there's no need to understand RPN to use its financial resources. But I'd never seen any HP12C owner that cannot help proudly explaining how to use it to anyone that asks for. [ENTER] key included!

About RPN mechanics: if you know how to use pencil and paper to perform computations, than you already know RPN well. Simply use [ENTER] when you finish writing one number and are ready to begin writing the other. In fact, I add an equals sign when writing an algebraic expression, but I cannot remember any moment I needed to write an "equals" sign when actually performing addition, subtraction, multiplication ort any other math operation. And that was the basic line I took when trying to understand RPN: if I know how to solve an expression, I'll be able to find its numerical result by using RPN-style keystrokes.

I think I have already written something like this sometime ago... a year or more, perhaps.

My thoughts. And my 2ยข, too.

Cheers.

Luiz (Brazil)