the three-value Miller index notation. This syntax uses the indices h, k, and l as directional parameters.

By definition, the syntax (hkl) denotes a plane that intercepts the three points a₁/h, a₂/k, and a₃/l, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell (in the basis of the lattice vectors). If one or more of the indices is zero, the planes do not intersect that axis (i.e.,