English: The points P₁ and P₂ are two points of the projection sphere and symmetrical with respect to the equatorial plane (red). With the crystallographic stereographic projection, both points are projected onto the same point of the equatorial disc, marqued as a cross for P₁ (north hemisphere) and a circle for P₂ (south hemisphere). As an example, the central angles NOP₁ and NOP₂ are different. Thus, central angles between two points must be read differently on the Wulff net if they lie on the same hemisphere (see Wulff net central angle 2.jpg) or not (see Wulff net central angle 4.jpg).