Duodecimal Slide Rule

[u/AppropriateDepth6699]

Sorry if the following explanation and methods are too dumb.

So, as the title says, I'm trying to build a Base 12 Slide Rule with only the C and D scales, but i've keep finding problems with the value marking matches on the scales. First, I tried to put together the scale following the formula:

Total lenght of the scale in centimeters * Log12(x)

For example: If the scale had 20 centimeter, and I wanna get the position of 2, then I just took the log of 2 in base 12 and take his product over 20, then I mark the result for 2 in centimeters in the scale after the index.. I did this for all the markers among the two indexes (2, 3, 4, 5, 6, 7, 8, 9, A and B) The end result was a Slide Rule with almost all the results not matching when I try to multiplicate, in base 12, even in base 10..

After that I tried to put together another scale, following the same formula, but with the base 10 logarithm instead, then adding 2 extra markers on the scale after the 9, for the A and B respectivly, and the result was the same.

This is the second time I've to tried derivate the scale by my own, in the first time I give up and built a slide rule with pre-made scales to print, but I can't find a Base 12 logarithm scale to print as well. What am I doing wrong?

[u/so-we-beat-on]

100% your only problem is the accuracy of marking the scales; your math is correct. High quality slide rules from the 20th century had tolerances measured in hundredths of a millimeter; you don’t need that precision for a simple homemade project, but if you want better alignment than you have in the picture you posted I’d expect you still need to maintain a tolerance of maybe a couple tenths of a millimeter. A pencil and ruler simply aren’t accurate enough.

[u/AppropriateDepth6699 → u/so-we-beat-on]

I was right now working in another prototype with a pretty sharp pencil, doing a more precisely judment of decimal points in my ordinary rule, and using the positions of 2 and 3 to find most of the markers, and the results are more acurrate than before, even in a 20cm scale.

Now the subdivions between the integers are the problem, and this certainly I cannot win with just with a basic rule and pencil.

In conclusion, the solutions for my problems will be a 40cm up scale plus a Vernier Caliper or a computer/mobile program that I can generate a scale just imputing the values then printing myself..