This tool can find the center of something with a maximum width of 30mm. The sides allow you to draw lines from 3 to 10mm distance from the edge, in 0,5mm increments.
The distance to the edge is exactly below the edge of the tool. So the distance to the edge is exactly where your drawn line starts.
This tool is public domain. Solid Works Part file and STEP provided. Enjoy
The author hasn't provided the model origin yet.