This is why it is critical to distinguish G from the vanishing point, as well as to move point F away from the left border of the picture. Points F and G may therefore be swapped at will, something Desargues himself does repeatedly in the course of his explanation on how to determine the image of a given point, invariably losing his reader who labours under the double misapprehension that G represents the vanishing point of the scene, and F some kind of distance point – or at least an accessory vanishing point of sorts. For the essential raison d’etre of the Distance Scale is to fold and unfold itself at will, accordion-like, admittedly not the easiest of procedures when it comes to the wooden engravings of Desargues’s time, but a mere trifle for today’s parametric software routines. Since all moves now take place within the box, points F and G are equivalent. The reflected image F1 of G0 relative to G is equivalent to the reflected image Gi of F0 relative to F.