Circular Slide Rule Kits 
Neal R. Wagner

Introduction

    A friend of mine (Bill Wahrmund) always wanted to teach children how to use a slide rule. He never tried it, but we thought about making paper slide rules of some sort. Later I thought a circular slide rule would be easier to make out of paper and has other advantages: no need to decide whether to slide left or right. I then found many web pages online devoted to helping a beginner construct a circular slide rule. Here is a simple and practical one:

    More advanced possibilities for circular and straight one are shown in:

    • Templates. A large number of templates for circular slide rules are given, along with many other templates. The first circular slide rule on this link uses a CD case as the basis for the slide rule.

    • Build Slide Rule. Build Your Own Slide Rule! A more complex circular slide rule.

    Those interested in slide rules can refer to The Oughtred Society. Also see the article on Wikipedia: slide rules and a great deal of other material online. I personally own two such watches (Seiko and Citizen) and always wear one of the other. This is just for show, since you need a magnifying glass to use such a watch. (For watches, you should look for an internal outer bezel, since the external ones get clogged up sooner or later.) I used slide rules for my undergraduate science classes, which was just before small calculators took over.

My Own Circular Slide Rule Kit:

    This page gives my own templates (see below) for constructing a circular slide rule, with scales C, CI, D, A, and K.

    Three Templates in Color:

    The template on the left was the first one I worked on. The one in the middle is the same with the scales squeezed together. The template on the right is rearranged for more accuracy with the A and K scales.


    Original: Demo, Inner, Outer, Pointer     		 
    Shrunk: Demo, Inner, Outer, Pointer     		 
    Rearranged: Demo, Inner, Outer, Pointer

    Three Templates in Black:

    Here are the same templates in black, with smaller headers. (Not using up as much ink.)


    Original: Demo, Inner, Outer, Pointer     		 
    Shrunk: Demo, Inner, Outer, Pointer     		 
    Rearranged: Demo, Inner, Outer, Pointer

    To "assemble" a kit, first pick out which of the six pictures you would like to use. Then for the chosen picture, print the three .pdf files given in links below the picture under "Inner", "Outer", and "Pointer". The "Outer" picture needs no cutting (although you could cut off the "Header" part to make a square). The other two should be carefully cut out. Finally fasten all three together with a binder clasp or in some other way. The pointer needs to be from some transparent plastic material. The other two could be the most durable material you have access to. The result should look like the initial picture (given as a .pdf under the "Demo" link).

    When I tried this myself using just paper and a standard binder clasp, the results were very disappointing. The various parts weren't precisely held at a central point, and that was a serious defect, making the slide rule unusable. Better would be to print everything on a firmer material, such as plastic, to carefully drill a small hole exactly at the right position, and to use something like a binder bold that would position everything exactly and centrally.

    It was clear to me that this "enrichment" project would need children familiar with decimal numbers, especially the decimal point, and multiplying and dividing by powers of 10. Whether this would work for, say, actual middle school children remains to be seen. I now think it would take a precocious child or an interested high school student. When I tried this out with a high-school age person (or maybe he was in college), the results were not as good as I expected. He lost interest fairly quickly. You need not to expect instant enthusiasm from everyone.

    Ten Pointers on One Page:

    How the Pictures Were Constructed:

    I wrote programs in the Postscript language for these templates. Then I used software to convert them to .pdf form. Here are a few of the Postscript source files. These are for the "Demonstration" versions. To get the others you just comment out a few of the calls to construct parts. Anyone interested in using Postscript in this way can look at my own materials related to learning the Postscript languge: Postscript. After some adjustment, it becomes easier than you might expect.

    For the versions in black, I removed all Postscript color stuff, along with a few other simplifications, to get in the middle case:

Fancier Circular Slide Rule Kit:
    A Professor at Sam Houstan State University, Joel W. Walker, liked my demonstration of building a circular slide rule, and he created a much more complex one himself (a fantastic job!). He told me that he didn't realize how easy it would be to program in "bare" Postcript and how suitable Postscript would be for this task (again, check out my introduction to Postscript):


    		 

    Here is Dr. Walker's Postscript code for the main slide rule:

      Circular Slide Rule, a very complex 300-line Postscrift Program.

      If this code looks daunting, impossible to learn to write, you should realize that Postscript is more like assembler code: not so hard to write but hard to read. This particular application is very repetitive, so you mainly have to figure out how to do one scale and move on from there. I greatly admire Dr. Walker's spiral at the center of his slide rule. His code is very complex and extremely well-organized, much better than the Postscript code I write.

    Making an Actual Slide Rule:

      Dr. Walker made it trivial to separate the three parts of the code, just by commenting out a few function calls (the .ps files below can be opened in most browsers and can be converted to .pdf files):

      Original:             SR.ps,             SR.pdf
      Inner part only:  SR.inner.ps,     SR.inner.pdf
      Outer part only: SR.outer.ps,     SR.outer.pdf
      Pointer only:       SR.pointer.ps,  SR.pointer.pdf

      There is also a section headed by "% draw frame and headers". Commenting out each line of this section (by inserting "%" at the start of each line) gets rid of the frame and external comments.

      No frame: SR.noframe.ps, SR.noframe.pdf

(Revision date: 2022-11-23. Please use ISO 8601, the International Standard.)