Planck's constant
Planck's constant, denoted by the symbol h, has the value 6.626 x 10-34 m2 kg/s. It sets the characteristic scale of quantum mechanics. For example, energy is quantized in units of h multiplied by a particle's characteristic frequency, and spin is quantized in units of h/2
. The quantity h/2 appears so frequently in quantum mechanics that it has its own symbol: 
.