## Friday, May 22, 2009

### Bleg: Find Φ's Calculator

I lost my calculator. It's an HP-15C, a gift from my father back in 1984. It has my last name and social security number engraved on the front in the upper right corner.

You bit heads will know what a big deal this is. The HP-15C is long out of production. It cost my father around \$150 25 years ago, but it now sells on ebay for over twice that amount.

Owning an HP-15C was a big deal in high school, helping me to solidify my position as King of the Geeks. I lost count of the number of times I had the following conversation:

Φ Friend: "Can I borrow your calculator?"

Φ: "Sure."

[Pause.]

Φ Friend: "Where's the \$%*! equal sign?"

Sometimes the frustrated borrower would sit through an explanation of RPN notation, but usually, they would go find someone with a TI.

In college, an HP-15C wasn't quite the big deal. The HP-41, with its detachable modules, and the HP-48 graphing caluclators were not uncommon. But I stuck with the HP-15C. The calculator took me through my entire undergraduate engineering curriculum. It proved most useful in circuits, where we were expected to solve 8x8 complex matrices in the course of an hour's exam. Complex matrices weren't native to the HP-15C, but the Advanced Functions Handbook gave the programming instructions that would find the solution.

(Question: Has anybody else noticed that mathematicians use TIs while engineers prefer HPs? Why is that?)

Once out of undergrad, most of my mathematics work involved the use of MATLAB. So the HP-15C found itself underemployed. But I used it enough that it found it's way to my desk at work, then back home, then back to work again. Usually, this wasn't especially deliberate. It just got tossed in the laptop case with the other stuff.

So it took me a while to notice it was missing. Something minor would come up, and I would look around for it at home. "It must be at work," I'd think. Sometime later, I would look around for it at work and think, "it must be at home." Or I wouldn't have my laptop case with me and assume that it was there.

But finally its absence became sufficiently noticeable that I made a comprehensive search. No luck. Where had it gone?

If it had fallen out of my case during my normal routine, I'd likely come across it again. If someone found it in the parking lot, he would turn it in to the school. I suppose someone could have taken it off my desk -- I'm in a cube farm, and my desk isn't locked -- but my fellow students are trustworthy, and the custodial service people would be unlikely to know its value.

Could it have been lost on my trip to Orlando? I called the rental car agency and hotel; they didn't have it. I called the airports, but they give stuff away after 30 days, and I didn't realize how lost it was until it was too late. I called the airline; also no luck.

In a fit of remorse, I bought another calculator last week. It's an HP-35S. I bought it from a 3rd party Amazon vendor; Amazon gave me a \$30 dollar rebate for signing up for one of their credit cards, so my out-of-pocket cost was only \$22. I chose the HP-35S because it appears to be the most powerful calculator permitted for use on the FE exam, which I have the ambition to take some day. It does almost everything the 15C does, like statistics, numerical integration, and equation solving. It's complex number functionality is actually superior: it displays a number's real and imaginary parts simultaneously, whereas the 15C would only show one at a time. It also allows operations in polar format; while the 15C would do a polar conversion, all operations had to be in rectangular format. The calculator also does vector operations, but this feature doesn't seem very powerful.

It's biggest shortcoming is: no matrix operations. But it will solve 3x3 linear equations; I'm not sure yet if these equations can have complex coefficients.

But I still miss my HP-15C. The new calculator has that plasticy made-in-China feel to it. And I really liked the wide keyboard layout rather than the long layout, because I can reach all the keys with my thumbs without moving my hands. I'm not sure why HP would abandon that format, except that it's slightly less compatible with a two-line display.

Kirt33 said...

Ha - my uncle (also an engineer, maybe a few years older than you) was down this week. He showed us how to use a slide rule.

Φ said...

Wow! Just this week, I happened to try to teach my daughter how to use my old Accu-math 550. I'm not old enough to have actually used it myself, so I had to go looking up instructions on the internet with only modest success, and in any case she didn't have the patience for it.

I did use an E6B circular slide rule / flight computer a lot back when I was planning cross-country flights. I wonder if anybody still bothers, what with ubiquitous computers.

PeterW said...

Hey, my dad has one of those, and I remember learning the odd notation you needed to use it. Never knew that it was a big deal.

I discovered, btw, that if you push the on and divide buttons in quick succession, you get an odd set of symbols that proceed as you press the buttons from top left to top right, and so on down the grid. Have you ever tried that, or is it an isolated bug?

Φ said...

PeterW: I never noticed that issue. If I ever get my calculator back, I'll give it a try.

Kirt33 said...

Unfortunately, the slide rule has no way to display "80085". I bet the HP-15C can handle it.