A proper rotation refers to simple rotation about an axis. Such operations are denoted by ⁠ C n m , ⁠ where C n is a rotation of ⁠ 360 ∘ ∘ n ⁠ or ⁠ 2 π π n , ⁠ performed m times. The superscript m is omitted if it is equal to one. C 1 is a rotation through 360°, where n = 1. It is equivalent to the Identity (E) operation. C 2 is a rotation of 180°, as ⁠ 360 ∘ ∘ 2 = 180 ∘ ∘ , ⁠ C 3 is a rotation of 120°, as ⁠ 360 ∘ ∘ 3 = 120 ∘ ∘ , ⁠ and so on.