The zone axis (**ZA**) is the direction lying in all the planes shown in
the slice of reciprocal space represented in the diffraction pattern, i.e. the vector
perpendicular to all the **g** vectors in
the pattern.

Take any two **g** vectors, **g**_{1} (*h*_{1}*k*_{1}*l*_{1})
and **g**_{2} (*h*_{2}*k*_{2}*l*_{2})
from the diffraction pattern. The zone axis is given by the vector product::

The zone axis is parallel (or nearly parallel) to the electron beam direction.