1. A circular target for forming guidance indicia on a radiographic image of an inclusion contained within a substrate, simultaneously with exposing radiographic film to form the radiographic image, comprising: a plate of radiographically pervious material bearing radiographically impervious masking material for forming the guidance indicia on the final radiographic image; and means for enabling an observer to ascertain the precise location of the target on the substrate, wherein the radiographically impervious masking material is arranged such that at least some of the guidance indicia is arrayed about the perimeter of the target as a series of spaced apart graphic entities.