Some easy but very helpful part if you have a Mr Beam II laser cutter. I'm using it as easy reference because the working space is a little bigger than the actual place the laser can go to.
Put this in the corner on your lower-left and the crosspoint of the two inner sides is your origin. This way you can work easy with common coordinate system instead of the sometimes inaccurate camera.

If you make two, it's also very easy to kind of frame your work piece and align it to your x axis. Distances are:
x_dist=6,0 mm
y_dist=7,5 mm

I made it with PLA again it's very easy to make and this way it really is good enough.