Archive: Computer Collector Newsletter / Technology Rewind, Jan. 2004 - March 2006

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LED calculators rule her house

by Evan Koblentz

This week, we took a road trip to visit Katie Wasserman, a collector of vintage calculators in the New York City area. Her collection includes more than 300 pieces! Many of the systems are really computers, of course. Here is her story. (Her web site,, includes many manuals as well.)

EK: What is your professional background and how did you get into collecting calculators?

KW: I was a math and physics major in college, but a year before I got there I bought an HP-35 as soon as they came out, in fact I was on the waiting list for about six months as I recall. As you can imagine, I got a lot of use out of it for those four years and beyond. After working in a physics laboratory for a short time I went back to school, this time in computer science. I started working as a computer consultant sometime during grad school and have continued ever since. About five years ago I felt the need to collect "something" and since the only thing that I appeared to know something about, and had a dozen or so of, were calculators so that was it!

EK: You have more than 300 pieces. Which are your favorites and why?

KW: My favorites are the ones that have something unique about them. Probably my most favorite is the Wang 500. It's got several unique things about it: a very unusual ROM memory made of hundreds of long enamel-coated wires wrapped around iron cores; a super-fast single-bit CPU built out of SSI logic chips; and of course tons of really cool-looking colorful keys. Also, I really like the Olivetti Divisumma 18 because it's "a work of art". Another is the Heathkit OC-1401, a relatively unknown air navigation calculator that appears to be modeled after the HP-35 but designed eight years later. Internally it uses three interconnected microprocessors to implement the basic five-level stack RPN calculator, the navigation functions, the display driving, and the keyboard scanning functions.

EK: What key pieces are you still looking for?

KW: There are only a few other calculators that I'm still looking for, but if you publish what I want it'll only serve to push up the price of them on eBay! :)

EK: One of your more unique pieces is a Swiss version of the Enigma machine. Tell us about this machine, and how you came to own one.

KW: I've always been fascinated with the German Enigma machine and Alan Turing -- the man generally credited for breaking the code it generated. Somewhat before I seriously started collecting calculators I was looking to purchase an Enigma at auction. But the price was a major deterrent -- not to mention the potential bad karma that comes with such a WWII relic. :) In researching various Enigma versions I came across the NEMA and found that they had recently sold at auction for significantly more reasonable prices. Being Swiss and made after WWII it didn't have the negative connotations, it also didn't have much (if any) use as almost all the NEMA's (640 of them, I think) are still in mint condition, so there was little risk of getting a bad one. I found a dealer who sells and auctions them in Switzerland and arranged to buy one directly from him.

[Editor's note: for more about the NEMA system, visit or get an emulator at]

EK: In what directions will you take your collection next?

KW: Aside from a few calculators that I'd love to find, I don't know that I want to expand it much further. I'm thinking about potentially donating much of it to a museum because it doesn't get much pubic exposure in my dining room (even if it is nicely displayed with all calculators in ready-to-play-with working condition).

EK: What do you think about today's calculators? Which ones will be considered "collectible" in the future, and why?

KW: Nothing made today seems destined to be collectable. There seem to be three reasons for this: extremely high production volume -- they're all made in the millions; really bad production quality -- they're not going to survive for very long; and I don't think that people get attached to them like they used to, they lack the cachet that they had in the early 70s.

Most calculator collectors that I know are in their 40s and 50s. They are the people that savored these machines when they first came out and followed their progression as they got more sophisticated and less expensive. Younger people don't look at these devices as much more than something that you need when taking a math class. I wonder what will happen to the "collectable" value of calculators when my generation is focusing on how many daisies they can be push up. :)

EK: You don't just collect calculators; you actually repair them in great detail. What are the common steps for keeping vintage calculators in good shape?

KW: Aside from HP models, my collection is all pre-LCD calculators. That means that they all use good-sized batteries, often rechargeable ones, to power the display (LED, vacuum florescent, Panaplex, etc). Over time almost all batteries leak and/or outgas, especially small alkaline and NiCad cells that are used in pocket calculators. These chemicals corrode the copper traces on the calculator circuit boards and plated electrical contacts. Making sure that the batteries are removed or checked regularly is critical to keeping them in good condition. Storing them in low oxidizing environments will help as well but this is nowhere near as important as proper battery care.

Beyond that each manufacturer/model has their own unique set of common problems: decaying rubber components, failed capacitors, fried resistors in the charging circuit, etc. There's a lot to learn about how to fix these and that's a big part of what I do and why I enjoy this hobby.

EK: This question may spark a holy war, but it's fun to ask: in your opinion, which is single best calculator ever made?

KW: Since I don't really have many current models I'm going to frame this question in the context of vintage [and] collectable calculators.

I'm not quite sure what you mean by "best", best constructed, best functionality, best looking? HP calculators -- as a group -- are largely considered among collectors to be the leaders in the first two of those. In fact many (most?) calculator collects only collect HP calculators, I have almost all of them myself in duplicate. But I don't think that any of the HP calculators (with the exception of the HP-01 watch/calculator and maybe the "Voyager" series (HP-10C, 11C, 12C, 15C and 16C) would be considered among the best looking. I think that many Sinclair calculators look great and as a group I'd say that they are the best looking, but construction quality (except for the Sovereign) and functionality are horrible. The Compucorp 300 series machines look really cool, are very well constructed and have superb accuracy (with a sort of quirky user interface) but are simply way too big. There are lots of candidates for the "single best". But since I do have so many of them (actually 400+ when I count duplicates) and I could use any of them I want on a daily basis, perhaps the one that I should select as the "single best" is the one that I use every day. And that's the HP 32SII. It's not a beauty, it's far from the most powerful calculator, it has very little memory and it has no I/O capabilities. But it's very well made, does pretty much everything that I need, has an easy-to-read display and is simple enough to learn fast and know completely.