I have a long standing fascination with calculating devices of any sort. Math is innately beautiful to me. And, the elegance and complexity of the objects that we have created to study it simply magnify that beauty.

I have built, played with, or own several different sort of calculating devices. These have included a simple Abacus while teaching our daughters math, and wooden Napier’s bones. More complex devices have been out of my ability and price range so far. These include:

## Babbage Analytical Engine

The is the mother of all mechanical calculators and is, in fact, a hand-cranked programmable computer. Charles Babbage designed (but did not build) this enormous device in the 19th century. A full history and description can be found here online. I would LOVE to have even a working portion of this magnificent device. Too pricey for me in solid brass… I have found some plans to 3D print parts, though, online. I may give that a try in the future.

## Curta Calculator

This little mathematical hand grenade has been on my wish list for a LONG time. Unfortunately, these go for $1,500 to$2,500 on Ebay. Yeah, I don’t think so. But hey, good news!! Marcus Wu (from the video) has put all the 3D printing plans for a Type I Curta online. I will definitely be giving this a shot with my printer. I might even need to upgrade printers just to get this done.

## Slide Rules

For 400 years, the humble slide rule was the tool of choice for scientists, engineers, and nerds of all persuasions. Only the advent of the electronic calculator was able to eclipse them. I just missed the slide rule era (going through high school in the later 70s). However, I have acquired a few (and I know how to use them) via Ebay. That site is mildly addictive; they should have a posted warning. My modest slide rule collection includes:

• Accumath 400
• Keuffel & Esser Co. K12 Prep
• Keuffel & Esser Co. 4081-3
• Keuffel & Esser Co. 4088-3
• Keuffel & Esser Co. 4097 D
• Keuffel & Esser Co. 4181-3
• Perrygraf 15” circular
• Pickett 120
• Pickett 300
• Pickett N515-T
• Pickett N803-ES
• Pickett N902-T
• Sun Hemmi 1447
• Sun Hemmi 1462H

The sliderules that are still on my bucket list are either the Keuffel & Esser Co. 4160, the Sun Hemmi 257, or the Post 1491. These rules permit stoichiometric chemical calculations (in addition to the other normal sliderule functions). I will keep an eye on eBay… However, they tend to go for more than $100 - so I’m not holding my breath. ## Electronic Calculators My very first calculator was a TI-57. Man, those red LEDs could burn through a set of batteries really fast. I have owned lots and lots of disposable calculators (you know,$5.99 and throw it away or lose it after awhile). Some calculators, though, are more enduring. Scattered around my desk at work, I have a small menagerie of prized calculators. This includes:

• HP 11C - In my opinion, the best pocket calculator of the 20th century
• HP 35S - A fairly worthy heir to the 11C
• HP 48S - My newest acquisition; a graphing RPN scientific calculator
• TI-30X II - Great for crunching numbers in dirty laboratories (I have about six of these)
• TI-36X Pro - A pretty close match to the HP 35S
• TI-84 Plus - Meh, I never really feel the need to break out a graphic calculator (that is what computers are for).

Other calculators that I wouldn’t mind having would include a HP 32S and a HP 42S. I also use calculator emulators on my mobile devices. On my iPhone, I use an HP11C emulator from RLM Tools. One my Chromebook, I use the official Hewlett Packard 15C emulator. Both work as good as the originals.

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