# Identifying poles on a stereogram through use of the Wulff net

To identify poles, find two great circles that intersect at the desired pole
*hkl*. Find the two zone directions [*u*_{1}*v*_{1}*w*_{1}] and [*u*_{2}*v*_{2}*w*_{2}] of these two great circles
by, in each case, identifying two poles lying in these zone directions, and
then using the Weiss zone law condition to determine the two zone directions.
The desired pole *hkl* is then the normal to the plane *hkl* which contains the
directions [*u*_{1}*v*_{1}*w*_{1}] and [*u*_{2}*v*_{2}*w*_{2}]; this can also be determined from the Weiss
zone law condition.

In general, directions such as [*u*_{1}*v*_{1}*w*_{1}] and [*u*_{2}*v*_{2}*w*_{2}] are referred to the real
space lattice, while normals to planes (*hkl*) are referred to the reciprocal
lattice.

However, since for cubic crystals, the normal to the plane *hkl* is parallel
to the vector [*hkl*], the algebra required is equivalent to taking cross products
to determine the zone directions [*u*_{1}*v*_{1}*w*_{1}] and [*u*_{2}*v*_{2}*w*_{2}], and then taking a cross
product again to determine the desired pole *hkl*.

So, for cubic crystals and stereograms of cubic crystals, we can drop the distinction between the real lattice and the reciprocal lattice. Therefore, for example, we can identify poles on stereograms of cubic crystals using vector addition, e.g.: