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I have recently acquired an HP35. It really looks like new and barely used (even the silvered band is intact).

The serial number is 1143S8596 (no 08596, just 8596 after the "S")

It is the second model, with the key funtions not printed on the keys (unfotunately not red dot), with just "Hewlett Packard" in the front sticker.

The back sticker is in Spanish.

It does not have the "5" key bump: Was this bump only present in "made in USA" calculators?
It does not have the famous 2.02 bug...again, was this bug only present in USA calculators?

Thanks and kind regards

Hi Ignacio,

I was hoping to see some experts popping up with clear answers to your questions….

In the mean time here are some fact about the different versions of the HP-35 (I recommend this article: Remembering The HP-35A, it is packed with details I’ve not seen elsewhere, such as HP internal memos).

1] the "5" key bump: according to the HP memo page 23 of the article above, it was decided with the introduction of the HP-80 in January 1973 to remove the bump, so all units built in the USA until the existing stock of keys with bump was used have the bump. Which means according to my observations: all 1143A, 1230A and almost all 1249A have the bump, late 1249A, 1302A and higher don’t have it. For the units built in Singapore the production of the HP-35 started in the second half of 1972 (exact date??) to address international markets outside of the USA and I don’t now if they started with the new keys or with the ones with the bump and then transitioned to the new ones.

2] the famous 2.02 bug: according to the second HP memo page 24 of the article above: all units built with a prefix starting with 1302A and higher are bug free, units with a lower prefix seems to have the bug if they were not returned for repair. Again no word about units built in Singapore. But your unit may have been returned and fixed.

3] front label: the “Hewlett-Packard” front label was replaced by “Hewlett-Packard 35” after the introduction of the HP-80, so all 1143A, 1230A, 1249A and early 1302A have the “Hewlett-Packard” front label. So it’s normal if your 1143S has it also.

Btw, it seems you have got one of the very early HP-35 built in Singapore. Would you mind posting some pictures showing details of the front, back and battery compartment?
Hi Didier,

I appreciatte very much your answer!!! I was considering to remove the word "easy" from my post;-D, until I saw your answer. It is impressive. I am going to print the article you mention and I was not aware of.

Do not doubt that I will post some photos. You will see that it is in a very nice state and looks like new. In this moment the calcualtor is at home...I shall try to do it during the week-end.

Again thanks for your detailed answer. Now is my turn to read the article and post the photos.

Kind regards

Some details about the start of the calculator production in Singapore:
  • April 1970: Singapore site opening to build core memories. (source: Measure Aug-Sep ’70 – p.10 & Measure Jun-Jul ’70 – p.15)
  • July 1972: No mention by Bill Hewlett of calculator assembly at Singapore: "We now employ 675 people there, about 60 percent of whom are assembling core-plane memories for our computers. [..] The remainder of HP Singapore is devoted to the assembly of special diodes and some LED displays." (source: Measure July 1972 - p.15)
  • February 1973: First mention of calculator assembly at Singapore: "Likewise, the APD people who have worked closely with the HP-Singapore plant in setting up comparable calculator production there for markets outside the U.S. report a similar gung-ho spirit. Some of the APD team are pictured at top, the Singapore assembly crew at right." (source: Measure February 1973 - p.8)
  • October 1973: Bill Hewlett wrote about Singapore: "Within the last year two steps have been taken that changed the pattern of production. The first was the decision to manufacture all the hand-held calculators for markets outside the U.S. in Singapore." (source: Measure October 1973 – p.15)
(06-25-2015 11:48 AM)Didier Lachieze Wrote: [ -> ]I recommend this article: Remembering The HP-35A

Thanks a lot for sharing the interesting read.

Quote:Since you had to press the “loop” steps yourself by
pressing the same sequence of keys over and over
again it became a challenge to work out the most
efficient stack manipulation sequence possible to
reduce the number of loop keys to press.

Appendix E – TI SR50 Competition, HP Analysis


[d/r] key - converts degrees to radians and radians to degrees depending on position of D-R switch.
This operation can be accomplished on the HP-35 by the following:

Convert degrees to radians:

DATA [ENTER↑] 180 [ENTER↑] [\(\pi\)] [÷] [÷]

Convert radians to degrees:

DATA [ENTER↑] 180 [ENTER↑] [\(\pi\)] [÷] [×]

The same could be accomplished without using the [ENTER↑] key:

Convert degrees to radians:

DATA [\(\pi\)] [×] 180 [÷]

Convert radians to degrees:

DATA [\(\pi\)] [÷] 180 [×]

So why wouldn't they propagate the shorter solution?


as promised, please find the HP35 pictures in the following link:

Unformtunately, the back sticker (in Spanish) was removed by the seller (not the original owner, whose name is typed in the "property of" sticker) attempting to repair it...but it worked perfectly when I recieved it. I tried to "stick" it the best I could. I bought it as "not working", but it was perfect.

You will see that I have added some pictures of sales documentation related to the HP35 (letters, leaflets, folders, informs, etc...some in Spanish) (bought in another auction)
Please, if you want any other picture, please let me know.

Kind regards

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