HP-35s Scientific Calculator Review

The HP-35s Calculator's Keyboard and Display.

An Engineer's Take on a 35th Anniversary Edition That's a Whole Lot More than the Original.


Tool, Not Toy

Too many calculators these days are designed to sell to parents of schoolkids, not to professional users. The HP-35s is a real tool for the professional, and the serious student.


The HP-35s Calculator

Looking Backward to Move Forward

The HP-35s calculator is a 35th anniversary tribute to the original HP-35 calculator. The HP-35 was the first hand-held scientific calculator, and a revolutionary device in its time. The HP-35s is much more than a simple retro look back at the past triumphs of Hewlett-Packard. It's a design for the working professional, a market that has been practically forgotten by calculator manufacturers in the face of the rise of the microcomputer and the growth of the educational market for high end calculators at ever lower grade levels.

Before I go into all that, let's look at the HP-35s and what's in the package.

The HP-35s inside the hard case

What's in the Box, and What's Not

I've seen the HP-35s in two different retail packages. Both are vacuum-formed "bubble" packs, one larger, one smaller. Both include the calculator itself, a quick start guide, a manual on CD, and a case for the calculator. The case seems to differ between the two packages, with the larger one containing a rather solid "hard" case, and the smaller package appears to contain a soft-sided case.

The HP-35s Hard Case.
The very substantial HP-35s case.

What is not in the package is the full printed manual. This is an important part of any calculator as capable and complex as the HP-35. It has a manual in PDF format on the CD, but a printed manual makes learning the features of the calculator much easier.

Fortunately, all it takes to get a printed manual is calling and asking for it. Hidden in the back of the quick start guide, under Additional Resources, is the statement that if you simply call HP and ask for a printed manual they'll send you one. They're true to their word. I called and received a manual free of any charges, delivered by UPS only two days after I requested it.

I had started working my way through the calculator's features with the PDF file on my laptop. Once I got the printed manual I was able to move through it about three times as fast.

Inevitable Comparisons

It's obvious that the new HP-35s begs comparison with the original HP-35. A comparison to recent scientific calculators from HP and other manufacturers is also logical. For many HP calculator users, it is also logical to compare it to HP's other classics, such as the HP-65, HP-67, HP-41C, and HP-42.

I have been a user of the HP-41C series on practically a daily basis since 1983, so this is what leaps to mind first for me. Likewise, over the past several years I have been looking for a calculator to replace or supplement my HP-41 calculators. I have used calculators from HP, Texas Instruments, Casio and Sharp in my quest for my next calculator.

What It Is, and What It Isn't

The HP-35s is a dramatic update to the original HP-35. The original HP-35 had a feature set comparable to a very basic scientific calculator today. While some early calculators called themselves a "scientific" model with nothing more than the basic four functions and a square root key, the HP-35 had far more. It had trigonometric functions, inverse trig functions ("arc" sine, cosine, etc.) It could raise a number to an arbitrary power, change sign, invert, and do logs, natural logs, and antilogarithms. Plus, it had a memory to store intermediate or constant values.

True to its name, it had 35 keys and a power switch. Most of the keys had a single function, with some having two functions (trig and logarithm keys, for example.)It used HP's famous Reverse Polish Notation (RPN), giving it the equivalent of four additional memories in its stack compared to a standard algebraic calculator, and a simplicity of operation comparable to an arithmetic calculator. It had standard and scientific display modes.

The HP-35s of today does far, far more than this. Most of its 43 keys serve four functions. Aside from the classic scientific functions, it adds probability, statistics, complex and vector functions, and integration functions. The most significant addition compared to the original HP-35s is the addition of programmability. It has a generous amount of memory that can be used for programs and large data sets.

And this is where the HP-35s begs comparison with the high end calculators of HP's past. The programming system is very much like that of the HP-65, 67, 41, and 42. The memory in the HP-35s is far more than these calculators had in the base models. So programs can be much longer and more involved. The HP-35s has built-in data types well beyond what the old calculators featured, including 2-D and 3-D vectors, complex numbers and polar coordinates. Unlike the older calculators, the HP-35s does not have any means of transferring programs on and off itself. And, unlike the 40-series it does not support alphanumeric data directly (though there are ways of including text in programs as, for example, data entry prompts for the user.)

The result is that there has been criticism of the HP-35s for its lack of these features. Realistically, though, this is an HP-35 analogue we're looking at, and a hugely expanded HP-35 at that. A comparison to an HP-41 or HP-42 is extremely unfair, and in spite of its expanded memory, programming, and calculation features it's also unfair to compare it to the 60-series with their built-in card readers.

A more apt comparison would be the recent HP-30 and HP-33 models. The HP-30 was a basic scientific with a two line display, algebraic entry, and no programmability. I got one of these as a free add-on to the purchase of an HP printer. It was worth almost as much as I paid for it. I still have it, and it was my constant inspiration to seek a better calculator. Every time I used it.

The HP-33 is a far more capable machine. It's very similar to the HP-35s in features, internally. It's programmable, has RPN, supports complex types, and so on. Unfortunately it's in a package I consider unusable. Its keyboard was designed to look good in a package, not to be used. The HP-33 calculator keyboard's shape, response, and layout all drove me off in spite of the internals. It has a terrible inverted chevron shape, and mushy flat lump keys that run one into another. It's also fragile. All very poor qualities for a professional's tool.

The HP-35s as What it Is

My own impression of the HP-35s is that it's great. I'm really happy with it. I'm a working engineer, I do mechanical, electrical, and electronic design. I also do performance, reliability, and safety analysis as part of my design work. This calculator does what I need. The addition of complex and vector data types simplifies things for me considerably. On my HP-41CV and CX, I use programs to be able to deal with such values. The HP-35s supports them directly. I'll admit that not all the functions I would like to have built in for dealing with these values are built in on the HP-35s, but that is solved with short programs using the built in data types, far simpler than comparable programs on the HP-41.

The probability and statistics functions are similar to those on my HP-41s, and are just as usable. The enlarged memory means that I can deal with larger data sets than on the 41s, where I deal with matrices of about 200 values at a time. I can go up to four times as large on the HP-35s, though I'm unlikely to go quite so large, in part because of the effect such a large data space would have on program memory. Really large data sets are better handled on a regular computer, but where a large set of values are needed in an intermediate calculation prior to reduction down to a few results, the HP-35s has the space to handle it.

Physical Design

The return of some of the design principles of the earlier HP calculators is a very welcome thing. The keys are clearly marked. They feel good, you can tell what's going on when you press them. I was concerned that the HP-35s might feel cluttered, as it has even more keys on it than the HP-41 series, but in use this has turned out not to be the case. The layout is not perfect, but it is logical and I've not had any problems adapting to it. I routinely go back and forth between it and my HP-41CV and CX without problems. The calculator is a bit wide, compared to the older calculators, but it is also lighter and not as deep. I would like to see it lose about 4-5mm of width, but it is not a problem to hold and use for long sessions. I find it is more comfortable to grip it a bit higher on the case than my older calculators, as its center of gravity is higher up than the older units.

The raised edges on each side of the keypad serve their function of protecting the keys from inadvertant presses. The number of functions, and the colors used on the keys add a bit of complexity--I found shifting my eyes from looking at the yellow labels to the ones in blue when looking for a function to be difficult, at first. I've adapted to it, it was no more trouble to get used to this than it was to get used to seeing the different functions of each key when I started using the HP-41C over 25 years ago. Keeping a fair comparison between a new calculator and one I've been using most of my life is difficult, but fortunately I kept notes when I was learning the HP-41CX, they've helped me maintain some perspective.

In toto, as a hard core user of classic HP calculators, and a working professional, I really like using the HP-35s.

The HP-35s
HP-35s Keyboard and Display


The HP-35s design is a welcome change from the candy shop and science toy calculators the market has been producing for the past decade and more. Both inside and outside, it's a solid tool. It does not have all the functions of a high end calculator, but given its price and positioning in HP's line these are not to be expected. It's an excellent value for the price, I paid a retail price at a brick and mortar store, it can be gotten cheaper from online merchants. (I wanted to see it 'in person' first.)

The HP-35s can't be everything for everybody, I've heard complaints from civil engineers who find the functions of the HP-33 more suited to their work, for example. Assuming you can stand the HP-33 keyboard. For myself, as a mechanical and electronic engineer I find the HP-35s supports me in everything I want to do far better than anything else on the market at present. It does everything I'd want to do on a calculator that's short of what I'd want to model on a full computer system.

Blue Sky Thoughts

I hope HP looks to this design and their other past designs when designing new high end calculators. A rework of the HP-50 along the lines of the HP-35s would be very welcome. There are a number of features I'd like to see beyond what the HP-35s provides, in a high end calculator at a commensurately higher price point:

  • Data transfer ability built in. Card readers are old tech, nowadays; a USB port and Micro-SD should be part of a larger system. Maybe even Bluetooth or WiFi as options. I'd pay for it.
  • Alphanumeric abilities like the HP-41CX. There's plenty of call for this in larger, more complex programs. Yes, an inbuilt text editor, too. I'd use it.
  • Expand data types to include physical units. Meters, ohms, grams, you name it. Allow calculations on units alone, as well as on scalar values with attached units, and vectors with units. Conduct automatic unit conversions by switching between unit modes. E.g., changing from English units to cgs would automatically display all values in cgs terms.
  • Pack in emulator software, so I can run the same software on my computer and my calculator, or use my computer as a development system for the calculator (but don't reduce the ability to program the calculator itself!)
  • Bring back external ROMs in some form, whether soft or hard, so that different professions can customize the calculator to their needs through Application Packs. Open up the interface so that third parties can play, too (The PPC ROM and Synthetic Programming sold me my HP-41CX. I was a dyed in the wool TI-52 user before!)
  • A full set of paper manuals in the box. Like the HP-41, give me a general use guide and a very, very detailed guide on programming. Put copious example programs in the text, and even more on disk. Charge me extra for the option, if you like, and make a cheaper CD or DVD-only option for the student bookstores.

One More Thing

There's one other thing I'd like to see from HP. They need to get their products back into education. Having products that really distinguish themselves from the competition is a first step. Getting themselves into the textbooks and in the hands of technical students comes next. When I was in college, I made the switch to HP and RPN (grudgingly, at first) because I was at a disadvantage compared to my fellow students when I had no HP programmable. Working problems with algebraic entry was slower and more error prone than RPN. I was an expert in the other calculators, I'd taught classes in their use. I was put off by RPN. Until I actually sat down with a classmate and used his HP for a while. It took me about 5 minutes to learn, and about 15 minutes to get used to RPN. After a couple of hours with a borrowed HP-41C, I saw why the HPs were better tools.

I mentally kicked myself for not listening when friends told me to get an HP-67, then the HP-41C. By this time the new HP-41CX had been announced. I scratched together the money from my meager college student budget (a number of missed meals and a lot of mac and cheese helped) and bought the CX as soon as it became available. It was better. Not only were my grades improved, but what I could do with my calculator was much expanded.

Since then I've continued to use my HP-41CX, as well as a CV I got later. I still use them, but not so much from choice as from a lack of choices in newer products. The way I work right now, I like to have calculators at three different locations. Another HP-41 costs plenty these days, considerably more than a new high end calculator with supposedly better features. There's a reason the HP-41 goes for more, and it's not sentimentality.

The HP-35s is a huge step in the right direction for HP. Another step in that direction with a new high end calculator will allow me to happily retire my HP-41s in favor of calculators that are even better. I hope HP makes money hand over fist with the HP-35s--I think they deserve it--and I hope to see more great work come out of HP's calculator design group in the future.