HP 35 type 2



I aquired recently a HP 35 type 2, with only Hewlett Packard on the front and a point on the 5 key. It does not have the hole for the red indicator on the on/off switch on the keyboard.

When dismanteling this beaty to clean, inspect and rebuild the battery I noticed on the slider of the on/off switch (the black piece of plastic in which the gold contacts are holded and on the other side the button which portrudes to the keyboard with which you swith it on and off) an original looking red spot of arounr 3 - 4 mm diameter.

Question: Is this common in this type or is this part of an earlier "mix" from the previous owner. It came namely with the netadaptor and the manual of a type 1 calculator. The serial number on the back, bottom side states 1143a 02034.


HP probably originally had a bunch of red dot switch levers made and used them freely in the cases without the hole. I have also seen red dot switches where the red is a rectangular band of paint and others where it is a round area.


From the (excellent) "A Guide to HP Handheld Calculators and Computers" by W. A. C. Mier-Jedrzejowicz:

The first batches were made for use inside HP only - they have an (hp) logo printed inside the battery compartment. The serial number is printed on the back, between the two lower rubber feet, it is 1143A followed by the unit number stamped into the label in letters 1mm high. A batch of nearly identical HP-35s was made for a customer company who placed and order for them. Then the first HP-35s for general sale were made, still nearly the same, but with the unit number stamped in 3mm high digits. I believe that only about 10,000 of these "HP-35 with a hole" were made...
Does your unit have the HP logo in the battery compartment? How high are the numbers "02034" in the serial number? Regardless, if Mr. Mier-Jedrzejowicz is correct about 10,000 units being made, and you presume that HP numbered them sequentially starting from 00001, then your unit certainly appears to fall within the red-dot production run. If it is indeed a red-dot, the lack of the hole in the front case may be due to one of the following reasons:

1. The step to drill the hole (if indeed it was drilled rather than molded) was omitted in the manufacturing process. In that case, you have a rare gem indeed, akin to a mis-struck coin or mis-printed stamp.

2. The front half of the case was replaced by HP when the unit was returned to them for service. Perhaps the case was damaged by the original owner and sent back. Perhaps the owner sent it back to have the bugs (see below) fixed, and HP replaced the front case at that time for some reason.

3. The front half of the case was replaced by a previous owner at some point in the unit’s life. This owner used a type 2 case, as evidenced by the lack of the "35" on the front label.

I don't know of any way to tell which of the above it might be. Perhaps you should try to contact Mr. Mier-Jedrzejowicz. He posts here occasionally, a search of the archives should produce his e-mail address. Of course it may also be true as David suggests that you have a real type 2 that got a leftover type 1 switch. That would also be a nice rarity.

You stated that "It came namely with... the manual of a type 1 calculator". On what do you base this statement? If I recall correctly, the front cover of the manual that came with the red-dots was totally black and white, while the manual that came with version 2 and later showed red leds and the blue keys, I think. I have never seen a red-dot manual in person, and don't have a later version handy to check, so I may be off a little bit on this. What does the front cover of your manual look like?

Above I mentioned having bugs fixed. If you are not familiar, the early units (version 1 and some or all version 2) produced erroneous results for some problems. If you enter 2.02, press ln, then e^x on your unit, do you get 2. or 2.02? If the former, your unit was not fixed. If the latter, your unit was indeed sent to HP to be fixed, so they may have replaced the front case half at that time.

Edited: 23 July 2004, 1:04 p.m.


Hi Jeff,

Thanks for the long response. I have no website SO I try to describe the manual:
top 2 cm in capitel letters HP 35. Blow that on a blue background the HP 35 seen a from the front, you can read clearly the fornt label (Hewlett Packard) an the keyboard with the hole next to the on/off switch. The display of the calculator shows 1.234567809 35
If you want a picture mail me you r mailadress.
Looking at the inside, the plast molding seems fine, I would expect if they forgot the dril the hole ther would a center point or something like that.

The option of having been in repair: I do not know, there is no label of HP repair inside (I have another classic where a sticker was put inside with the service date).
And it does (still) have the ln E 2.02 bug. It gives the false 2 as an answer.
What I did nitice between this one and an type 3 HP 35 I have is in entering a negative mantenissa. In the new one you can enter the mantenissa and then hist the chs button and yoou get a negative mantenissa. On this one however the CHS has to be done BEFORE entering any number as mantenissa or it will not have any effect at all.

Also the net adaptor is said to be the small one of the type 1 model. The modelnumber is 82002A and is realy a differnt model compared to the netadaptors I have with the 45, 55 classic calculator I own.


Congratulations for your finding!

Let me just say that yours is sort of a "fossil", with the original, early ROM with bugs. There have been interest in obtaining an image of such historic (may I say prehistoric?) ROM. If that very special ROM image could be "revealed", then it could be run in some of the current emulators, and further studied and analyzed.

This situation is somehow comparable with the fictional finding of the DNA of a prehistoric animal.

If you please, I would suggest you to get in contact with Eric Smith. Peter Monta, or other microcode experts who regularly appear here.

Congratulations again!


My HP-35 is a type 2, serial no. 1249A03943 and it has the 2.02 ln ex result 2. bug. It also will not CHS after entering the mantissa. Maybe these ROM bugs are not so rare? How about others checking their HP-35s and sending in the results with serial numbers.


My 35V2 with ROM bugs has the same CHS behavior too (I don't have the calc with me at the moment to give the serial number). I think that the CHS fix was part of the ROM fix, not another variant.



The ROM bug versions are not that rare. Of all the type 1 and 2 machines that I have had, over a third have the ROM bug.


The serial is:

small letters ( 2 mm high) 1143A and then larger letters: 02034.

My other HP35 without the ln e 2 an d mantenisa bug has number: 1302S 92156


Hi John,

As collector I like to hang to this one for some time.
It has some nice other type 1 like characteristics:

Silver screws: present,
two piece backing plate (by battery compartment): present,
black two piece shorting clip: present, 1143A0xxxx serial number: present, bump on key 5: present, red dot manual: present, back label "HP35 INSTRUCTIONS": present, battery cover calling for HP03510 battery: not present, gray plastic case is unique to the red dot, allowing the smaller charger to fit snugly: present.


Metal LED frame: present, Soldered Circuit board to keyboard assy (not finger connected)not present is finger connected, Red plastic key frame: not present, white plastic, grounding plate inside back cover: present, gold colored metal key membrane: present, circuit board "00035-60010": present, red dot switch: only on the inside.


Jeff alerted me that in this thread he had quoted from my book. No problem - what good is a reference book if people don't refer to it? I just want to add that on my red-dots the hole appears to be molded, not drilled, so this is not the HP-35 equivalent of a postage stamp with missing perforations ;-)

Setting up a data base to which folks could submit serial numbers and characteristics, including bugs, would be neat! The claim that about 10,000 units with the hole could be checked properly,




Hi Wlodek,

I recognised the text (got your book last week via Guy Ball).

Wonderfull book, is realy my reference these week. To bad that HP does not drill, but "molds" the hole.


Wlodek and others --

I just got a 2nd version HP-35 working, which had been given to me by a co-worker. I opened the back, cleaned and re-greased the power switch (Radio Shck Lube Gel), and re-installed the two-piece spring shim that is required for operating the calc without charger.

S/N: 1143A 26472

The manual set includes an errata page listing the well-documented "exp ln 2.02" bug, among several others, but this calc exhibited none of them.

It computes more quickly than I expected -- faster than the functionally-comparable TI-30 from 1976-77 that I used to have.


Holy crud!! You want to sell it? Email me at perrybucsdad@alltel.net if so. I'd be willing to pay a handy sum for that HP35.



sorry to burst the bubble, but this is not unusual. The V2 (your model) just removes the "red dot hole" - the reason was simple: even with depleted batteries, the red dot would be visible and therefor being misleading (you could tell by looking at the display if the calculator was operational anyway). The V2 molding of the upper case part even has the "hole area" visible.
As for the PCB, to my knowledge, the V2 did use the same part and many of the V2s had the ROM bug - nothing special there ;)
Still a nice piece of history though :)


Thank you all for the responses.

For me, this is one of the nice reasons to collect and study the older HP calc's.

I do not see these nice discussions and almost "archeological" fact finding on TI SR50 machines, who are on it's own, also very nice examples of the technolgy at that time so I stick to HP machines mainly.

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