Story stick version of yardstick trammel

The modified pivot piece can be printed without supports and attached to the cone with a short piece of 1/8" dowel.  

I used PLA, but any filament should work. 

As in the original, you can use a ruler that is the proper thickness or, a strip of material that is about ¼" thick.

My need was not to make a circle, but, rather to compare distances between two points.  For example, if an item is an accurate rectangle, the diagonals will be identical.  So, for squaring assemblies, being able to compare diagonals can be very useful without having to resort to any sort of actual measurement.  

I am using it to help with squaring the mechanics of my MPCNC Primo.  The procedure is to mark a square, possibly using a shallow depression made by the router (e.g. a 1/8" roundover bit) and then using this tool to compare the diagonals.  

Two things have been changed in the original design.  First, the hole in the “pivot” has been enlarged to accommodate a 1/8" dowel, and then a small cone with a 1/8" diameter tip has been fabricated so that it will be fairly accurately placed into the routed depression.  This cone can be attached with a 1/8" dowel.  

Note that the acorn nut and the washer from the original design will be needed.

One could also use the original pivot design, which used a nail, of course, but by having a tip that approximately matched the depression, the placement is somewhat kinematic, possibly leading to more accuracy.