I don' get how this works. How exactly do you put the squares together? Stacking them (even with rotations by mutlplies of pi/2) will not detect the case when

I don' get how this works. How exactly do you put the squares together? Stacking them (even with rotations by mutlplies of pi/2) will not detect the case when every edge has the same kind of deviation from the straight line, right? Putting them edge to edge will assure every edge is straight and the same length (within observation limits) but may get you a rhombus which is not a square. Do you somehow iteratively combine both of the above?