Planck constant

radiation physics. Symbol h. The fundamental constant ratio of the energy of a quantum radiating from a black body to its frequency, = 6.626 069 3(11) × 10^-34 J·s with relative standard uncertainty 1.7 × 10^-7·
[Mohr P. J., Taylor B. N. CODATA Recommended Values of the Fundamental Physical Constants: 2002 (to be published)]
[Mohr P. J., Taylor B. N. Rev. Mod. Phys. Vol. 72:351-495 (2000)]
[Mohr P. Phys. Today Vol. 53:7, 11-16 (2000)]
[For latest recommended values, see http://physics.nist.gov/cuu/Constants/index.html](J·s=m²·kg·s^-1 in base terms.)

The rationalized Planck constant or Planck constant over 2 pi (i.e. 2π) = 1.054 571 68(18) × 10^-34 J·s; denoted by ħ, it is the atomic unit and natural unit of action.

It has been proposed
[Potnis V. R., Chai A.-T. Amer. J. Phys. Vol. 40, 767 (1972)] that the name planck be accorded to the m.k.s. unit of angular momentum, i.e. 1 kg·m²·s^-1, which is dimensionally identical to 1 J·s, although the latter relates to action, not momentum.