In addition to their other properties, all particles possess a quantity called spin, an intrinsic angular momentum. Despite the name, particles do not literally spin around an axis, and quantum mechanical spin has no correspondence in classical physics. In the position representation, a spinless wavefunction has position r and time t as continuous variables, ψ = ψ (r, t). For spin wavefunctions the spin is an additional discrete variable: ψ = ψ (r, t, σ), where σ takes the values; σ σ = − − S ℏ ℏ , − − ( S − − 1 ) ℏ ℏ , … … , 0 , … … , + ( S − − 1 ) ℏ ℏ , + S ℏ ℏ .