Rubber feet on 35s and general 1st impressions


Just got my 35s from e-walmart.

The display is slightly misaligned (no need to view all annunciators to draw attention to it).

CN: ...226 for those who care

Good to see the return of the continuous rubber foot at the bottom. Hope they finish this off with the upper feet on future revisions.

It sure is a pretty compact device (nice). Form factor is right on, minus the arrow keys. Slips right into shirt pocket, unlike the 33s due to its bulky foot pads.

Sure can't wait to see what the UNDO operation does. Hope it isn't supposed to enable the undoing of a basic operation like:


Because, it certainly doesn't :)

Most keys feel fairly good and responsive. Seems not to suffer from the missed keystroke ailment of past.

Not intuitive how to cross two vectors though. ...wait...vector support DOES mean it can do that right?

Perhaps the user guide in my vehicle will shed more light.


Good to see the return of the continuous rubber foot at the bottom. Hope they finish this off with the upper feet on future revisions.

Why do you prefer that? I liked the individual feet of the 41C and Voyagers better, though I don't have that strong a preference.


Page 1-11 explains UNDO. Actually, a rather useful command. It recovers a deleted entry rather than reversing an operation. For example:

123 <- (clears the 3)

<- (clears the 2)

UNDO restores the 3

UNDO restores the 2


Oops! The other way around:

UNDO restores the 2

UNDO restores the 3


I'm seeing a trend here, with the displays and S/N's. Just based on the big thread elsewhere about S/N's, and the prevalence of mis-aligned displays, I'd surmise that:

- Wal-Mart used their leverage on HP to get the very first batch of 35s units. Literally. Almost all of the really low numbers seem to be from Wal-Mart purchasers.

- The first batch or so had an alignment problem.

- The second batch went out to other smaller retailers (perhaps Samson, for example), and was a mix-n-match of mis-aligned and perfect aligned.

- The third batch was kept at HP and used to fulfill direct SMB orders from their website. There was perhaps another mix-n-match batch, but more perfect aligned units than in batch 2, and truly far fewer problems.

- Later batches seem to be just fine.

- Batch sizes are unknown, but seem to be in 500-1000 unit range.

- "Batch number" did not correlate to ship date. In other words, my unit came from batch 3, but my unit still arrived before some purchasers in batch 1.

Just educated guesses, but interesting nonetheless. If I'm right, it makes me wonder why they stopped selling them if the later batches were alright? Intriguing...




FYI--I ordered my 35s from HP-SMB on 7/14/07, and it was shipped on the 19th, S/N 72104035, display aligned ok. The guy at SMB said that the first shipment would consist of 2,500 units.

tm in Redwood City, CA


That continues to fit my theory. Mine, also direct from SMB at about the same time, was 4266, and had no problems either.



My unit (72103814), ordered from HP SMB, had a severly misaligned display. Two other users with serial numbers very close to and bracketing mine had no display alignment issue.

I am curious whether the 725x batches have this occasional display alignment problem.


can you post a picture of it to show us?



can you post a picture of it to show us?

Unfortunately, as I had mentioned in another post, I have already fixed the problem and didn't take any pictures before or during the disassembly. (Curiosity and eagerness to fix the problem...)

The display had a left to right upward slope. The rise was about one pixel. The right side annunciators were just barely being covered by the gasket between the LCD glass and the outer plastic display cover.


Good morning Bruce. I have unit from Walmart (s# 72500462) and display is not misaligned. I order first day available on walmart site.


Okay, so you guys shot some holes in my theories. ;-) I knew there would be outliers, though...



Your theory may still be good. I may be asymptomatic owner of otherwise good theory (or maybe I not intelligent enough (or blind) to see misaligned display) ;-)


Good to see the return of the continuous rubber foot at the bottom. Hope they finish this off with the upper feet on future revisions.
Ref. to Really Advanced Statics (Virginia, 1776), a tripod is the one and only statically determined body. So 1 broad foot a the bottom, 2 upper feet, ENTER, + ;-) may be a good reason to leave it this way.


My thought too, but translated simpler version. A tripod will not wobble. Try sometime. Sit on stool with four legs. If one leg have difference in length, stool wobble. Find stool with three leg. Chop off 1 inch of one leg, and stool will not wobble.



sorry I do not know a single word in Hungarian. But I hope you agree on calling your proposal the Hungarian method ;-)

Best regards, Walter


My friend Walter. I tell you what. I teach you a word of Hungarian. "Nem" means "No". So, nem, I do not mind it being called Hungarian method. Actually, I am honored. :)

In fact, it take me a while to figure out what you mean by "statically determined body", but then it made sense to me what you were saying (in Hungarian, we would call it literally a passive immutable body... yours sound better though). It amazing how words may be different with different language, but in math and physics, language really all the same, just different words to express same things things.

BTW, I found out about "statically determined bodies" when I was a child and could not figure out why three legged stool my aunt had would not wobble. My uncle was very mad at me when I saw off almost 10cm from it. Good thing I was cute little boy then or I may have not survived uncle Jozsef being upset at me. ;)


Sometimes, especially scientific or technical ones, terms are clearer in one language over the other, especially with English:

As an American, I've always been taught and used the term, "potential" for the "E" part of Ohm's law, E=IR, or less properly, "voltage".

But the German, "Spannung", which literally tranlated to English is "tension" is really a better word picture, a more accurate description I would say, than either "potential" or "voltage". I mean, it's weird to say, "There was (potential/voltage) between the pitcher and the hitter", unless both were standing where there will be an atmospheric electrical discharge in a few minutes.

Boy, I wish they'd fix the (English) terminology in quantum mechanics...


Hi, Ed,

IIRC there were signs warning for "high tension" at power poles. Did they change it to "high voltage"?

Boy, I wish they'd fix the (English) terminology in quantum mechanics...
What in particular? We gave you the Eigenvalues and Eigenvectors already, isn't that sufficient? ;-)

Regards, Walter



... good one.

I was actually thinking of "spin".

As to voltage and tension, it seems the overwhelming majority of time, "voltage" is seen over "tension". Perhaps you were thinking of Britain or other English speaking countries?

Edited: 7 Aug 2007, 11:00 p.m.


Sorry, the spin is called "Spin" here, too. This does help us to get the message it's something strange, because we don't have a German word for it. If you are in this topic, maybe you know the "Yrast-line", a nice example of some Swedish in QM.

Perhaps you were thinking of Britain or other English speaking countries?
Do you want to point out this way you are US-American? :-)


If you are in this topic, maybe you know the "Yrast-line", a nice example of some Swedish in QM

For the english speaking among us:

if you want "yrast" to sound swedish simply say "e-rast"


I've never had to say it (yet)!

Any involvement of mine with quantum mechanics generally stops with chemical physics. I can reasonably discuss atomic physics, but not nuclear.


That doesn't explain why a wide rubber foot on a calculator is a good idea.

A stool with two normal legs, spaced x cm apart, and a third lex x cm wide (and perhaps 2x-3x cm from each of the other two) will definitely be able to wobble.


That is what a former older colleague called the "intelligence of matter": Since rubber is softer than table tops, any small protruding parts will "adapt" under pressure, i.e. deform and/or wear down fast until the broad foot will rest flat on the table top (remember the most pressure is at the bottom, where the keys are pressed). - Quite similar behaviour may be observed with wrought-iron cafe-tables put on a gravel terrace.

Edited: 7 Aug 2007, 6:44 p.m.


That reasoning still doesn't seem to apply, for two reasons:

1) If it does wear/compress to sit flat in one particular position and orientation on the uneven surface, it will not sit flat in some other position and orientation on the same uneven surface.

2) There's no reason why the same wear/compression wouldn't happen with four feet, rather than two "normal" and one "long" foot.


I think in simpler Hungarian terms, what Walter trying to say is rubber will not wear, but conform to contour of surface. If you have four small pad, like 15C, unit will wobble with uneven surface. Now with three pad (even with one very long) unit more stable. Now yes it possible that with very uneven surface it will wobble, but that is outside of (I can't think of word...Walter can you help?)...well what we can and can not deal with.


I've never had a problem with a 15C or 41C wobbling on a surface on which the "long foot" calculator wouldn't.

The calculators I'm designing will have four feet. I suppose anyone that doesn't like that is welcome not to buy my calculators. :-)


... but that is outside of (I can't think of word...

... (most situations)?
... (most surfaces)?
... (the ordinary)?

Fortunately, English is often more flexible than even a long rubber foot.



Nevertheless, now I'm "at the end of my Latin", as people would say here. PLEASE!! We need a native English-speaking person (US-American, Indian?) to explain to Eric why 3 feet are superior to 4. He seems to refuse to understand, and may easily crash his calc project by this stubbornness ;-)


We need a native English-speaking person (US-American, Indian?)

Funny you should say. My Cherokee name is Agadvnv nasgiyai alisoqualvdi (or Hung like bear) ;-) I I thought Hungarian have too many consonants next to each other. How the heck is Agadvnv pronounced? I think it sound like leaking tire sound. ;)


Nem, Vincze, there was a trap hidden in my post, and you are the first bear who stepped into it :-))


I don't see how separate 3rd & 4th feet are in any way inferior to a very wide 3rd foot, with regard to stability.

The tripod analogy becomes inappropriate once one of the "points" of contact spreads to a line of contact (and one every bit as long as the spread between the other two points).

Take your camera tripod out on uneven ground, and rigidly attach a board at its midpoint to the end of one leg, perpendicular to that leg, and parallel to (and with a length equal to) a line connecting the feet of the other two extended legs. You'll find it no more stable than a "quadpod" with four equal-length legs.

With such a wide third pad, the question becomes moot.



I agree fully. The 32sii had broader upper feet, but the style was in line with the lower foot (pad).

Students who fail statics go on to design tables for cafes'. Particularly outdoor tables. Of all places (flooring) one would expect to find out-of-plane inconsistencies it would be a cobbled sidewalk cafe :)



Perfect. A good theory should not be ge given up by the fact, that nearly all implementations of the asymmetric tripod in terms of pioneer calculators were wobbly. In fact, we need to adapt the conditions under which wobblism(*) appears to reach the stability predicted.

(*) Oh, and I think this should not come under the eyes of a native english speaker *g*

Edited: 8 Aug 2007, 3:56 a.m.


I looked closely at the lower foot pad on my 35s. I noticed that even though the foot runs the width of the calculator it is not flat, only the (2) ends will rest on a surface. The center of the foot is warped inward toward the calculator. So, even though it has (3) feet, it behaves as if it had (4) feet. This must be due to a special de-wobblelization treatment of the lower foot to ensure it doesn't warp the other way :)


Good observation! HP could now go and rationalize production for some rubber material in-between both ends, ending up with a low cost pseudo-asymmetric 1 1/3 tripod. HP invent! :^)


This must be due to a special de-wobblelization treatment of the lower foot to ensure it doesn't warp the other way :)

The spec probably required "straight +0 -0.1" :-))

BTW, I never dared do invent such a word like de-w...on.


Okay.. although I am not native American, let me Let me try this again today when my mind is clear and not so tired and full of wine.
A three legged dog walks into bar... no wait. Wrong explanation.

Okay, I try again. A three legged stool or table will not wobble because the end of legs always form a plane. It that simple, but I know this a sophisticated group who not accept simple "Hungarian Method", (as Walter so nicely state this is) as answer.

To look at this mathematically, a three legged stool or table solves for a system of three equation in three variable, while a four leg table will change mind about which three of four equation to solve for the same three variable.

Pretend there a three legged stool or table sitting on three legs. Now add a fourth leg on some line out from the top of the stool to the floor. There is only one single length which will now just reach the floor. If the fourth leg is a little too short, then the leg will not contact, and the stool will pivot about two of the legs (wobble), or as in mathematical equation, it will change it's mind about which three of four equations to solve for. Also, if one leg a little to long, or floor is uneven, then when fourth leg come in contact with ground the stool will have to lift one of the other three legs off the floor making stool wobble.

Now let say that you have stool that had four *exactly* equal legs forming a square on the bottom of the stool, but now the floor is uneven. Now, there will be some way you should be able to adjust stool so that all legs (4) touch the ground and there will be no wobble. This like intermediate value theorem.

Now, one thing we also have to remember is that three legged stool not always very stable. So how do we offset this. One way is to extend out legs so that it very hard to tip over. Or, as HP do, they make one leg (rubber foot pad) very wide, and others small. This will prevent instability, except in most severe situation with sever angles, in which case, legs (or rubber feet) need to be longer (taller) respectively. That look funny on calculator though.

I hope that make sense, if not, I give up. :)

Edited: 8 Aug 2007, 12:43 p.m.


Also note that the problem of wobble will not necessarily be repaired even if the feet of a four legged chair or table are made to be perfectly co-planar...because the chair or table will invariably be placed on imperfect surfaces!


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