"The symmetry of the Normal Class of the Hexagonal System is as follows: The vertical crystallographic axis is an axis of hexagonal symmetry. There are six horizontal axes of binary symmetry, three of them being coincident with the crystallographic axes and the other three lying midway between them." — Ford, 1912

Symmetry of normal class

"The symmetry of the Normal Class of the Hexagonal System is as follows: The vertical crystallographic…

An illustration of military personnel measuring normal intervals.

Normal Military Interval Measurement

An illustration of military personnel measuring normal intervals.

Orthogonal projection of a closed plane-faced polyhedron.

Polyhedron

Orthogonal projection of a closed plane-faced polyhedron.

Orthogonal projection of a closed plane-faced polyhedron.

Polyhedron

Orthogonal projection of a closed plane-faced polyhedron.