Hewlett Packard

Hewlett Packard - the best calculators money could buy. Cream of the crop, they felt good just to hold.

HP wasn't the first to market, but it can be argued that they blew it open and sent it into orbit. (The HP 65 was the first calculator in orbit.) HP's functionality broke ground. And their great trendsetting ads simply sucked you in, promoting the idea that owning an HP 35, 45, or 64 made you somebody - combining technology and status in a new way. A decade later, Apple copied their tone for the Mac campaign, and then again with the iPod.

HP 19C

The 19C packed programmability and a printer in a handheld calculator from 1977 to 1979. It had more programming functionality than a 65, but lacked the convenience of magnetic card storage. On the other hand, Continuous Memory (CMOS) meant that you could at least preserve the program last entered, as opposed to a 25 which forgot everything when you turned it off.

I'd love to have one, but this 19C doesn't belong to me. The owner, a chemistry professor, asked me to build a battery adapter for it that would allow him to power it with replaceable AAs. I both managed to do so, and I also figured out how to modify an original HP "Sting" battery pack to do the same.

If you have a 19C (or the rare HP-10) and want to use it with replaceable AAs, email me at bobwolfson@gmail.com.

Above: Original HP Sting Battery pack modified to allow one to replace the batteries in it with any AA's.

Below: A hand-made pack that serves the same purpose.

HP 35 Collection

Any collector will tell you that it's an accomplishment to put together a full set of anything. I hereby congratulate myself for collecting a full set of all the generations of HP 35, the calculator that changed the world. (Thank you, Bob! I feel good about it!)

If you were alive then, you would know: there was before and after around this calculator. Before, nobody realized what was possible. After, you could see personal computing, way off on on the horizon, maybe, but approaching. (Moore had not yet expressed his law, so we didn't see the acceleration right away.)

If you ever used a slide rule, you know how much faster and more likely you were to get correct answers with the HP 35. The amount of power it put in your hand was stunning. And using RPN gave you a taste of the fundamentals of modern CPU operation. There could never be a going back.

HP 35 version 1 "Red Dot"

So, here's something rare: the first edition of the famous HP 35, distinguished by the little hole in the faceplate to the right of the power switch. When you slide the switch rightward to turn the calculator on, a red-painted part of the switch is visible through the hole -hence the name "red dot". Hardly a useful feature, so no surprise, HP discarded it after producing somewhere around 4500 of them.

Nobody knows, of course, exactly how many remain. But you can find a registry of sorts here: http://hp35.wz.cz/HP-35RD.html.

The serial number of this one might be 02967, but it's pretty hard to be sure because the first 4 digits are barely impressed into the label.

Most of the early 35s, including many of the version 2s, had a calculation bug that HP repaired for free upon request. (The classic test being when e^(ln(2.02)) turns out to be 2 instead of 2.02.) This one still has it, so presumably its innards are original.

This used to belong to one R Paulson, whose name and SS (which suggests he's from Minnesota) are inscribed inside the battery compartment cover. If you see this, R, please contact me and let me know the calculator's story!

HP 35 version 2

This is the first production run after HP eliminated the red dot at the power switch. This one has the nub on the 5 key, lacks the "35" on the nameplate, and has the buggy firmware where

2 = EXP(LN(2.02))

Even very smart people make mistakes from time to time.

HP 35 version 3

Essentially the same as the above, but without a nub on the 5 key and with the addition of "35" to the nameplate, this is the version that HP sold the most.

This is a particularly clean example that I decided to sell. It fetched $85 in 2013.

HP 35 version 4

One of the first calculators I collected.

Fully working, but has a blemish at upper right of the keyboard where an owners initials were removed, and the rear label is somewhat creased from accessing the screws beneath it.

HP 45

This is probably my favorite electronic calculator. It feels great to hold, works like a charm, looks great, features RPN, the manuals are a joy to read... I use it all the time.

This had no battery pack when I bought it, so I bought a standard black plastic 3-cell holder, trimmed it to fit the battery compartment, and wired it appropriately. Voila, a classic HP running on standard alkaline cells. They last way, way longer than the old NiCads!

I've learned how to build a much nicer AA battery since this initial effort, and if you want I'll make one for you. See my HP AA Battery Adapter page for details.

HP 65

The first programmable calculator, costing $800 in 1973. And programs could be recorded on little magnetic cards! Geeks made geek friends by owning one of these!

There were at least 2 variants of the HP-65. I don't know what dates or serial numbers correspond to them, but I have a S/N 1333A and a S/N 1604A that are different.

On the keyboard, they vary in the font sizes used for the shift-state text of the Enter key's row.

On the back, my 1333's S/N is inside the battery compartment, but the 1604 has it between the bottom feet.

HP 16C

A calculator made for programmers, which, though I am one, I don't know how to use. One of these days I'll have to spring for a manual from the HP Museum.

This unit is in mint condition.

HP 12C

A classic and I think HP's most popular calculator ever.

This one's pretty beat up, but it still works.

HP 21

This was a replacement for the HP 35. It's a bit more powerful and quite a bit smaller, almost palm-sized.

HP 22

This was a great choice for a business calculator until the 12C came out.

HP 25

Big brother to the HP 21.

This is a lot like a programmable HP 45. It can only record 49 steps, with no subroutines. It has no card reader, and no persistent memory so programs had to entered afresh every time you needed one. A large Application Programs manual supplied many compact routines for business and science.

Programs can have conditional logic. It can loop only about 2 times per second!

A short time after the 25, HP introduced the 25C with Continuous Memory.

HP 41CX

The most powerful version of the first handheld calculator with an alphanumeric display and keyboard.

It's a handful of power - very programmable and boasting: a "user" mode in which every key can be assigned a built-in or programmed function; keyboard templates on which to record the assignments; date/time/clock/alarm/stopwatch functions; external memory functions; and 4 ports for connecting pre-programmed modules and/or a suite of peripherals.

It's really an impressive machine, and has more the feel of a portable computer than a programmable calculator. And yet it faithfully adheres to the tactile ergonomics of the Classics and Woodstocks.

Yet it has one terrible usability flaw. You see, HP developed this calculator because they realized that the power of programming hinged on being able to execute functions by name. There are simply so many functions one wants to have to enumerate them or assign them all to keys. If you can't use memorable names, you can't get very far.

Consequently, the 41 had the notion of "executing" a named function and features an EXC key to tell it that the next thing you enter is going to be a function. But they gave the user two ways of specifying the function to execute: either press a key to which the function has already been assigned, or press ALPHA to throw the keyboard into a mode where keys correspond to letters instead of functions and then type of the name of the function to call.

This was a bad idea because most functions are NOT assigned to keys, and thus if you press EXC the most likely thing you want to do next is enter text! So why doesn't the 41 go into ALPHA mode automatically upon pressing EXC? But it doesn't.

Worse still is the consequence of forgetting to press ALPHA when you should! You wind up thinking you're entering text when instead you're executing functions and screwing up your calculation or the program you're entering. Not only is ALPHA mode the most useful state to enter after pressing EXC, it's also the safest.

So in my opinion, HP really didn't think this one through - pressing EXC puts you in a less useful, more dangerous state than it should.

HP 20S

This is now my go-to calculator! Great positive key feel and great functionality with CMOS memory and, believe it or not for an HP: infix entry instead of RPN!

HP 28C

This was owned by S.D. Carter. If that's you, please drop me a note!