 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.