Is the HP35s reliable?


I've been a TI user for about 20 years now, progressing through TI-81, TI-85, TI-92 etc. My TI-92 is now dying miserably and is just too large and heavy to cart around any more.

I sat down and wrote what I actually do and the HP35s appears to be a good fit feature-wise and I've always wanted to use RPN as it's more efficient.

Unfortunately there are less than favourable reviews from people complaining about battery use, dodgy keys and general reliability.

Are these rumors founded?


Hi Chris,

You can find a bug list here:

HP-35s bug list.

I'm not a power user by any means but there are some doozies on that list.

I've been told by a couple of the people here that the 33S, unconventional appearance aside (if you can manage to put that aside) is actually a more reliable machine if you are looking for straight RPN.


Nothing too horrible, especially compared to my TI92 which has some really annoying eye-poking bugs. Trig issues are slightly worrying but I'm not sure they will manifest themselves in my daily use.

Doing some research it suggests that all HP35s' are not equal. I wonder if there are a couple of versions floating around.

33s is missing a couple of things I'd like unfortunately :(

I could go for a 48SX/GX or possible a 15c but I can't get one for a reasonable price in the UK.

Edited: 17 Feb 2012, 11:06 a.m. after one or more responses were posted


Have you considered the 50g instead? It's not expensive and has lots of power. Most probably more than you'll ever need.

Another option might be the WP 34S, a DIY project discussed here in some detail.


I considered the 50g but it's a bit overkill for me and 2x the cost of the 35s.

My main application areas are pretty simple EE stuff (worst case complex numbers, some trig and solving sim. equations). I'm interested in developing a few simple programs to make the routine stuff slightly less laborious.

WP34S sounds good but I just want something that works these days (I'm getting old and lazy).

Edited: 17 Feb 2012, 11:20 a.m.


My main application areas are pretty simple EE stuff (worst case complex numbers, some trig and solving sim. equations).

I doubt the HP-35s handles the following. The HP-50g does.

1) V1 - V2 = 10*Ix 
2) V1/j20 + (V1 - V3)/20 + V2/10 + (V2 - V3)/-j10 = 0
3) V3/j10 + (V3-V2)/-j10 + 2/-45 + (V3 - V1)/20 = 0
4) Ix = -V3/j10
where j = sqrt(-1) and 2/-45 is 2 angle -45 degrees.


This is true. However, my TI92 does/did this. I use it once a year perhaps. Most circuit analysis problems can be pretty much solved without very little math if you know how.


I've used the HP 35s for about 3 or 4 years now. It's never failed me. Although what i use it for are quite less complex in terms of the mathematics involved, but in terms of physical build quality and keyboard I have had no problems what so ever. I had a TI-89 titanium before the HP 35s, and while powerful it was just too much for what I needed.

Battery use? I had mine on the batteries that came with it 4 years ago and just last month changed the batteries. Only because the battery symbol had been on for about a month.

Dodgy keys? Maybe. My plus key creaks for some reason when i press it lightly, but nevertheless all buttons feel the same after all these years.

General reliability has been great for me. While I do keep it in its (hard) case, I'm sure the HP 35s can take a good beating sliding around a backpack.


If you use complex numbers, you'll be *much* happier with the 50g than with the 35s or 33s.


Well, not as easy as the 50g, but it can be done.

The biggest necessity is matrix capability, but fortunately someone on the internet has done something already:
A Matrix Multi-Tool for the HP 35s

So we have to re-arrange the equations a bit and write down the co-efficients for input into the matrix:

Data for matrix A:

1i0; -1i0; 0i0; -10i0

0.05i-0.05; 0.1i0.1; -0.5i-0.1; 0i0

-0.05i0; 0.1i0.1; 0.05i0; 0i0

0i0; 0i0; 0i-0.1; 1i0

Data for column vector b:

0i0; 0i0; -2Ø-45; 0i0

Even 0 entries must be entered as 0i0 when working with complex numbers.
For -2/-45, the symbol Ø represents the theta symbol on the 35s. You can enter it like that as the 35s will automatically convert it to -1.41421356237i1.41421356237 (unles you have set it to polar mode, in case which all the other inputs are converted).

After about 15 seconds, the solution vector reads:







Hey, that's great! If they address at least some of the bugs (in order to show their good will) I'll buy one again!

Best regards,



Yes, I am disapointed that after almost 5 years they still haven't fixed the bugs. For instance entering long programs like this matrix one or Pauli's 700+ line game is difficult when the checksum cannot be releid upon as I have had to spend time to check and re-check to ensure correctness.


That's exactly what I felt when I read the remark in your complex functions program, linked below:

"Program length and checksum are not provided as they make no sense on this calculator"

Edited: 18 Feb 2012, 8:47 p.m.


WP34S sounds good but I just want something that works these days (I'm getting old and lazy).

Version 2.2 of the 34S certainly does this now.

Version 3 is much improved but not quite stable now, although it is very close.

Download the emulator and give it a whirl. It is possible to buy a repurposed device where all you need to do is to apply the overly.

- Pauli


I'll try it in the emulator and see!


Complex number handling is very cumbersome on the 35s, and it lacks some really useful features like direct polar to rectangular coordinate conversions, which I'm sure you know can be very useful in EE. I much prefer my 33s in these regards, and it's cheaper than the 35s.


I noticed but from what i can see, it's possible to use a program to convert from polar -> rect and vice versa.


But why go to the bother when you can do it directly from the keyboard ? And there's so many annoyances on the 35s, such as not having separate primary keys for STO and RCL or the negative sign on the number / mantissa not being centered, or the left / right shift arrows that should be up / down etc. Anyway, I hardly ever use it compared to my 33s and 32SII.


... it's possible to use a program to convert from polar -> rect and vice versa.

I have that program loaded, but I find it easy enough to just change the display. LeftShift, DISPLAY choose no. 10 for Polar or 9 for Rectangular. (shortcuts: "LeftShift DISPLAY .0" for Polar, "LeftShift DISPLAY 9" for Rectangular).

When in Rectangular mode, you can still easily enter polar values and they are automatically converted to Rectangular. And vice-versa when in Polar mode.

I find the actual entry of complex numbers the easiest on the 35s compared to all other HP's I have worked with. You do just type 123 i 45 ENTER.

On the 42s it is: 123 ENTER 45 SHIFT COMPLEX.
On the 32S/SII and 33s a complex number takes up two stack levels and each operation has to be preceded by the COMPLEX key.
On the 50g entering in vector form is easy, but to get "123+i45 one has to do: 123 ENTER 45 LeftShift i * +

However, very few functions on the 35s support complex operations (unlike the 42s or 50g, where they form an integrated part of the functionality), but I have written some routines for that, listed in this other forum post: HP 35s complex operations



Interesting stuff!

I've bought a Casio FX991ESPLUS (sorry chaps!) and an HP35s. Will see how I get on with both!


FX991ES PLUS arrived earlier today. Not a bad machine for 15GBP! Probably end up using this in the end.

Surprised to find that it's pretty much the same as my SmartCalc 300s but fixes all the horrible complaints I had about that.

Awaiting HP35S delivery still...


In my opinion, the 35s is decent calculator, much better than what some "purist HP-fans" tends to express. There are some quirks, but nothing that has bothered me, during the 4(?) years of daily use.

The trig error (close to 90 deg), is of little importance, unless you plan to send a rocket to the moon, where the error in digit position 8 might be of importance.

The keyboard has a good quality and the display is OK (but not perfect, as it is difficult to distinguish "8" from the angular symbol theta).

/ Lars B (29C, 41CV, 19BII, 35S, all in daily use)

Edited: 20 Feb 2012, 4:29 p.m.


Have you used the 33s as well?


Incidentally, the trig bug was first noticed on the hp-33s. I like this calc, but I got somewhat disappointed after that. I wasn't on my way to Mars, but I was checking the results of my own trig program for the HP-12C Platinum upon the hp-33s when the discrepancies arose. At first I thought my results were wrong, until I decided to doublecheck the results on my good old HP-32SII.


Yepp! I used it for 2 years, but was highly annoyed of the graphic design of the symbols on the keys and the frontplate. The locations of the keys seemed somewhat "cluttered" and the ENTER key was way to small. I put the 33 in a drawer and bought a 35s instead. I haven't used the 33 since then.

I previously had both a 32s and a 42s at my old workplace, so i'm familiar with those as well.

BTW, the 33s is -ugly-, and that might also bias my judgement....


I originally felt as you did about the appearance of the 33s. But in using it on a continual basis, I found it to be much more pleasant to use than the 35s. The appearance no longer bothers me and the keypresses on the 33s feel better. I have even begun to like the HP's selection of unshifted keys for the 33s. It seems easier to calculate on and program than the 35s. In fact, it is the one I reach for most of the time, unless I need something only the 50g can do.


I'm with Lars. The 33s just looks too much like a prop from a Flash Gordon episode, although I know there's a good machine underneath those looks. As much as I like to think of myself as purely rational, I admit that I am in love with the retro look of the 35s, and I have yet to be affected by any of its "bugs". It's my "daily driver" calculator. I also like the action of the 35s keys better than my 28s and 50g. I think the feel of the 35s keys are as good as those on the 45, 25, and 41C, although I know some folks have had problems with key presses registering on their 35s. I'll keep mine, thanks.

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