After the substituents of a stereocenter have been assigned their priorities, the molecule is oriented in space so that the group with the lowest priority is pointed away from the observer. If the substituents are numbered from 1 (highest priority) to 4 (lowest priority), then the sense of rotation of a curve passing through 1, 2 and 3 distinguishes the stereoisomers. A center with a clockwise sense of rotation is an "R" ("rectus") center and a center with a counterclockwise sense of rotation is an "S" ("sinister") center. The names are derived from the Latin for 'right' and 'left', respectively.