On Apr 28, 3:06*pm, dbeitzell wrote:
snip
who on earth puts thirds on their rulers? *NOBODY!

Umm... Nerds do, of course. What you want is an "engineering
scale" (or rule) - not an "architectural scale".
http://en.wikipedia.org/wiki/Engineer's_scale
You can find them at engineering and/or art supply stores. It's a
ruler with a triangular cross-section. One of the scales is 30 ft. to
the inch, so one third of an inch is 10' on the scale. DW
appropriated one of mine for... get this... QUILTING!
Nowadays, it should be easy enough to create & print one out on your
computer.

But if your printer isn't accurate enough, (or you're stuck on that
desert island your math teacher always warned you about...) there's an
old trick I learned in design class that will get the job done.

1. On a piece of paper (or label stock if you plan to stick it on the
end of a ruler for future use) draw two parallel vertical lines about
6" long, exactly one inch apart.
2. Near the bottom of the two lines, line your standard ruler up at an
angle so that the one inch mark is on the first (left) line, and the
2-1/2" mark is on the second (right) line. Make tick-marks at 1-1/2"
and 2".
3. Repeat step 2 near the top of the two lines.
4. Draw vertical lines through the two sets of tick marks.

You now have an inch divided EXACTLY (or as nearly as practical) into
thirds. The same method can be used to divide an inch into just about
any number of equal parts. Fifths of an inch? - no problem - or use
the 50 scale on the engineering scale above. ;-)

Doc Smith