When u have a 3d printer and ur X Y possitioning isnt perfectly in the middle u can use this design to messure ur possition and alter it in ur slicer. for example in simplify3d its called origin offset.

with my new delta printer i had to set my origin offset using this design cause my first prints wernt in the middle and when i would print large prints it would go off my printbed.

hope u guys can use this.