According to Robert Swinney :
Karl sez:
" To me, this is like saying I'd rather drive my car in reverse on the
freeway. Does HP still use that RPN logic? What on earth is the reason
for it and WHY would anyone like it? ( I know - I'm just troolling)"

My guess is that in the early design days it was not economically feasible
to produce chips to support direct algebraic entry. Thus, RPN was developed
as a crutch, more or less, to facilitate HP's entry into the calculator
market.

RPN happens to be how computer languages mannipulate math
internal to the programs. It is much more compact, so it allows you to
do more with a given amount of hardware -- and if the hardware can be
increased, you can add more functions, instead of tying it up handling
parens.

I got my first HP (a 45) back when those were new. I've gone
through a few of the subsequent ones, finally stopping at the 15C (for
scientific calculations), and the 16C (for computer math manipulations).
I've got one of each in my belt pouch, and a spare 15C in a Ziploc
baggie in the shop, where it can be used without lubricants or coolant
soaking into it. (Put it in facing the back of the baggie where there
is no printing.)

We were taught by HP (General Bullmoose ? ) to manipulate a "stack"
in order to accommodate their klunky entry system. And so, RPN became the
de facto standard. Besides, it had great appeal for those that would have
us believe "computer math" was beyond the reach of ordinary intelligence.
Like, "Hey, if you ain't smart enough to learn to do backwards arithmetic,
you got no business with a calculator anyway."

Before the HP-45, I was using a Cannon printing calculator with
algebraic notation (but no trig functions or other fancy stuff).

So -- I vastly prefer the RPN to algebraic calculators.

FWIW, the unix calculator programs bc and dc both use a variant
of RPN. And the GUI interface one, "xcalc" has the option to use either
algebraic notation or RPN. Guess which I have it set to? (And the
keyboard shuffles when you change the notation system to look either
like a HP 15C or some TI calculator of the same period.

Enjoy,
DoN.
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