XYZ Probe and Code for Mach 3 anyone?

Having been away from cnc for a while, I’m days from delivery of a new router. One of my old problems was getting a decent zero to the edge of the material and whilst I know this doesn’t trouble many of you, it does me. So I am eager to make and code for one of these cool little XYZ edge plates. The ones on YouTube have an undercut which you slide onto the edge of the work and the machine then locates a hole to find the edge of your job, then touches the edge off the plate to find rest of the dimensions for zero.

I’d love to make one of these and having a manual machine for jobs like this, I would like to try and build one whilst I wait for my machine.

Does anyone have plans for one but equally as important, the code needed to enter into Mach3 to actually get it to work?

Any help appreciated.

Chris