Calliper ruler

Calliper ruler attachment  for metal rulers that are around 1mm thick and 26.2mm wide(for the 30cm rule) 1mm thick 19..2mm wide (for the 15cm rule). celco and studymate work well any that fit those measurements will work too. 

A 18mm x 3mm magnet fits in the slot at the back. 

The magnet helps the lower jaw stay in place not move too much when your measuring something and is good for picking fallen screws, blots or whatever else you drop.

The top jaw cover the 1st cm on both rulers turning them into a 29cm and 14cm rules. so read the cm marking 1 lower then they show (I couldn't find a better way so i chose to cover 1cm, but its easy to remember after using it a few times).

both parts are friction fit and can be removed with easy, if you want a permanent fit glue is a open and if I made them any tighter you cant move the lower jaw without a hammer or other blunt object.

There is some bridging going on and some may be get in the way, I've made a bunch of these and you just need a little force to shove the rule in. you can easily remove any stray strains by hand (I use a knife get a clean edge). the lower jaw will wear out with use especially if your using a harden steel ruler like I do  

This is an attachment to a ruler and not a replacement for quality Vernier Callipers. both jaws do have some wiggle more so the lower about +/-0.5mm for the 30cm set and 1mm for the 15cm set. Both sets will still give you the overall  dimensions of  of a thing and make it easier to read those measurements and transfer them working similar to a ruler stop. 

Never use this to determine any critical dimensions please use the proper tools for the job.