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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 2nd Jan 2004, 10:18 pm   #1
ppppenguin
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Default HP calculators & reverse Polish logic

I have a HP35 calculator (the 1st ever scientific pocket calc in the world unless somebody knows otherwise) which I picked up years ago at a BVWS auction. Works well. If it weren't for the short (but rechargeable) battery life I might well use it every day.

They cost over £200 when new in about 1971! I saw one when it was new, securely locked into a fixture on a desk at Imperial College.

I love the reverse Polish logic as used in the older HP calcs. Any other fans out there?
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Old 3rd Jan 2004, 12:38 pm   #2
Paul Stenning
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Default Re: HP calculators & reverse Polish logic

I had to use reverse Polish logic when I was programming with Forth at work a few years ago, and I had trouble getting my head around it initially. Once you get to grips with it it's OK, but when you have to work with languages using standard and reverse Polish logic at the same time, it's easy to get confused....

For thse who don't know what reverse Polish logic is, in essence you have to store the numbers before you can do anything with them. It came about because of the way early calculators and programming languages like Forth use a stack for storing numbers.

With the HP calculator (as I understand it) you enter the first value and press [STORE], then you enter the second value then press the button for whatever function you want to do with it and the stored number. So if you pressed [2] [STORE] [2] [+] the display would show " 4 " .

From a low-level software point of view it's simpler because the instructions come in a more usable order.
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Old 3rd Jan 2004, 1:06 pm   #3
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Default Re: HP calculators & reverse Polish logic

And you can never get mismatched brackets because there aren't any. For a calculation like:

(4+3) x (5+2)

you would do the following:

4 ENTER 3 + 5 ENTER 2 + x

This is exactly how you would do it by hand, work out the contents of each bracket, then do the multiplication. It always works for any expression on a HP calc provided you work from the innermost brackets outwards. The stack is not deep enough to have more than a couple of pending operations so:

(4+3) x (5+2) x (6+1) x (7+3)

would be done as:

4 ENTER 3 + 5 ENTER 2 + x 6 ENTER 1 + x 7 ENTER 3 + x

and not as:

4 ENTER 3 + 5 ENTER 2 + 6 ENTER 1 + 7 ENTER 3 + xxx

which is logically equivalent and correct but would overflow the stack.
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Old 4th Jan 2004, 1:23 pm   #4
peter_scott
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Default Re: HP calculators & reverse Polish logic

Hi Ppppenguin,

I totally agree with your RPN enthusiasm.

RPN calculators are just magic in comparison with
the usual four function + equals jobs.
The RPN stack almost seems to read your mind regarding what you want to do next and if you
make a mistake with data entry or a wrong operator,
RPN is totally forgiving whereas with four function
you invariably end up re-starting from scratch.

Long live RPN,

Peter.
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Old 4th Jan 2004, 8:39 pm   #5
RobinBirch
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Default Re: HP calculators & reverse Polish logic

Hi,
I learnt RPN for the first ever calculator I owned, a Sinclair Scientific. I loved it. I got hold of a working example several years ago and was astounded at how slow it was. It's funny how memory plays tricks . I then had several HP41s which I also thought were wonderful.

I have also had a lot of fun with Forth and similar languages which has led me to really having a " thing " to do with RPN.

All power to the people who put this system together.

Robin
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Old 6th Sep 2006, 1:26 pm   #6
valveaudio
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Default Re: HP calculators & reverse Polish logic

I also have a HP35, and now use a 32S. Great!
Another non-technical advantage, I always used them at work and they never went missing because no one knew how to use them!
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Old 6th Sep 2006, 6:51 pm   #7
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Default Re: HP calculators & reverse Polish logic

The Anita 1011 IC and LSI also used RPN



ALAN
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Old 6th Sep 2006, 8:46 pm   #8
Nickthedentist
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Default Re: HP calculators & reverse Polish logic

My (elderly) physics teacher had one until the early 90s, but had to abandon it when the keyboard begain to fail. He too apparently loved the "reverse Polish logic" (we all thought he'd made that term up).

His had a little built-in magnetic strip reader for storing programs on, I think

Nick.
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Old 6th Sep 2006, 8:55 pm   #9
Phil G4SPZ
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Default Re: HP calculators & reverse Polish logic

Quote:
Originally Posted by RobinBirch View Post
I learnt RPN for the first ever calculator I owned, a Sinclair Scientific. I loved it. I got hold of a working example several years ago and was astounded at how slow it was.
As a student in the mid 70's, I and most of the chaps on my course built Sinclair Scientifics from kits at £14.99 each. I still have mine and it still works. We used to run calculator races by entering the same randomly-chosen number and all pressing the 'log' button at the same time. The one that displayed an answer first won the race. The calculators usually took about half a minute and frequently came up with different answers!

These brave machines would also have a bash at calculating the value of infinity. Entering 1+0 then 'divide' usually gave a numeric answer, different each time of course... it was a lot more fun than a slide rule.

Phil
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Old 6th Sep 2006, 11:35 pm   #10
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Thumbs up Re: HP calculators & reverse Polish logic

Quote:
Originally Posted by ppppenguin View Post

I love the reverse Polish logic as used in the older HP calcs. Any other fans out there?
"Any other fans?" Absolutely!
Setting aside the (trivial?) issue of avoiding stack overflow -which is a hardware-specific limitation anyway - the one thing that I really appreciate about RPL is that it is so logical! Unlike the English language , in RPL you effectively state what it is you want to process, define the process and then perform the operation. The concepts flow naturally. With the English language, there are so many bits of information that you have to "store" in a scratch-pad in your memory until you then find out what qualifiers apply to these bits and then what you you have to recall what the defined operation was. For example, take the very simple instruction "open the green door". In RPL this becomes "door, green, open door". No ambiguity, no confusion. Totally logical.

Al.
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Old 7th Sep 2006, 12:29 am   #11
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Default Re: HP calculators & reverse Polish logic

Quote:
Originally Posted by ppppenguin View Post
I love the reverse Polish logic as used in the older HP calcs. Any other fans out there?


My 16 years old HP-42S works as well as on the day it was bought, which is to say perfectly! At uni people would look at you oddly if you choose any calculator brand but HP. Texas Instruments did run some programs to try to convince people to switch, but with little to show for it (at the time).

HP still makes Reverse Polish Notation calculators, even though these days they appear to allow for the sacreligious modus operandi called 'algebraic data entry' in addition to RPN.

Once you get to try RPN there is no going back as far as I know. I still struggle and stutter my way through the parenthesis, whenever I am forced to do calculations on a lower form of pocket calculator.

Frank N.

PS: There were several versions of HP pocket calculators going back to the mid seventies, which were equipped with magnetic card reader/writers for storing data and programs.
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Old 8th Sep 2006, 2:23 pm   #12
vahakuja
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Default Re: HP calculators & reverse Polish logic

Hi,
My first calculator was also HP35 (I still have it!) and I learned to use RPN. After that I have had quite many HP models and actuallay the RPN is the only "keying" which I can without thinking individual steps. Last 20 years I have been using HP12C and 15C models.
The RPN is excellent, no-one want to borrow your calculator!

BR
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