## A few of my favorite: Slide rules

,I link to photos hosted by the International Slide Rule Museum, a really great resource. Unfortunately, they don’t set IDs on their pages for specific rules, but luckily I only discuss two brands: Pickett and Faber-Castell.

I love slide rules nearly as much as I love HP calculators, and much like HP calculators, I have a humble collection of slide rules that is largely complete. While I keep them around more as beautiful engineering artifacts than anything, I *do* actually use them as well. These are a few of my favorites, from both a conceptual standpoint and from actual use.

- Pickett 115 Basic Math Rule:
- This is, by far, the simplest rule that I own. It lacks the K
^{1}scale that even the cheap, student 160-ES/T^{2}has. Aside from the L scale, it is functionally equivalent to a TI-108. But, to be fair, the TI-108 has two functions that nearly all slide rules lack: addition and subtraction. And, true to the name ‘Basic Math Rule,’ the Pickett 115 has two linear scales, X and Y, for doing addition and subtraction. Additionally, it has one scale-worth of Pickett’s ‘Decimal Keeper’ function, which aids the user in keeping track of how many decimal places their result is. All in all, it’s not a particularly impressive rule, but it is quite unique. Faber-Castell made a version of the Castell-Mentor 52/80 (unfortunately ISRM’s photo is not that version) with linear scales as well, and I probably prefer it in practice to the 115. The 115 just has a wonderful sort of pure simplicity about it that I appreciate, however. - Pickett N200-ES Trig:
- This is basically the next step up from the aforementioned 160-ES/T. The 160-ES/T is a simplex with K, A, B, C, CI, D, and L scales. The N200-ES/T is a duplex model that adds trig functions with a single set of S and T scales, and an ST scale. It’s a wee little pocket thing, the same size as the 160-ES/T, and it’s made of aluminum as opposed to plastic. It’s nothing fancy, but it handles a very useful number of functions in a very small package. The N600-ES/T does even more, but it becomes a little cluttery compared to the N200-ES/T’s lower information density. Good for playing with numbers in bed.
- Faber-Castell 2/83N Novo-Duplex:
- The 2/83N is, in my opinion, the ultimate slide rule. It has 31 scales, conveniently organized, and with explanations on the right-hand side. Its braces have rubberized strips on them, and are thick enough that the rule can be used while sitting on a table. The ends of the slide extend out past the ends of the stator so it’s always easy to manipulate (I don’t have any Keuffel & Esser rules on this list, but they had a clever design that combatted this problem as well, with the braces being more L-shaped than C-shaped). The range of C (and therefore everything else, but this is the easiest way to explain) goes beyond 1-10, starting at around 0.85 and ending around 11.5. The plastic operates incredibly smoothly (granted, I bought mine NOS from Faber’s German store a few years ago, that had to have helped), and the whole thing is just beautiful. Truly the grail slide rule.
- Faber-Castell 62/83N Novo-Duplex:
- This feels like a complete cop-out, because it is essentially identical to the 2/83N, except smashed into half of the width. You lose the nice braces, you get a slightly less-fancy cursor, and you lose precision when you condense the same scale down to half-width. But you end up with something ridiculously dense in functionality for a small package. Even though it’s essentially the same rule as the 2/83N, I think it deserves its own place on this list.
- Pickett 108-ES:
- This was the piece I’d been looking for to essentially wrap up my collection. It is a circular, or dial, slide rule, and it is tiny – 8cm in diameter. It’s much harder to come by than the larger circular Picketts, particularly the older 101-C. Circular rules have some distinct advantages – notably their compact size (the 108-ES is the only rule I own that I would truly call pocketable, and it cradles nicely in the palm of my hand), and the infinite nature of a circular slide. The latter advantage means there’s no point in adding folded scales, nor is there ever a need to back up and start from the other end of the slide because your result is off the edge.
- The 108-ES, by my understanding, was a fairly late model, manufactured in Japan. It is mostly plastic, and incredibly smooth to operate – moreso than non-circular Picketts that I’ve used. The obverse has L, CI, and C on the slide; D, A, and K on the stator. The reverse has no slide, and has D, TS, three scales of T, and two of S. I can’t help but hear “I’m the operator / with my pocket calculator” in my mind when I play with this thing. It really packs a lot of punch for something so diminutive. The larger 111-ES, of the same sort of manufacture, is also quite impressive with (among other things) the addition of log-log scales.

- If you’ve never used a slide rule before, the names of the scales won’t mean much. I’d suggest reading the ISRM’s Course on How to Use the Slide Rule and their Glossary for a full description of scales, but here are some basics: C and D are logarithmic scales used for multiplication. CF and DF are the same, but they start further down the line to effectively make the slide ‘longer’. CI and DI are the reciprocals of C and D, you can probably guess what CIF and DIF are. A and B are squares of C and D, K is cube. S and T refer to Sin and Tan, ST is a combined sin/tan scale for numbers low enough that they’re effectively the same. L is a linear scale for reversing the log. LL scales are log-log scales used for arbitrary exponentiation. ↩︎
- Pickett released yellow and white slide rules, largely standardized by the model number ending in ‘ES’ for ‘Eye-Saver’ yellow, or ’T’ for white. ↩︎