English: Measuring the central angle between two points P1 and P2 on a stereographic projection using the Wulff net. A transparent sheet has been tacked in the middle of a Wulff net and the points are drawned on the transparent sheet. The transparent sheet has been rotated until both points P₁ and P₂ lie on the same meridian (see Wulff net central angle 1.jpg). The angle is measured by counting the graduation along the meridian between both points (here, 2° steps: the angle is 92°).