Atomic unit of mass in SI units.
value = amu [value,sigma] = amu
amu returns the SI value in kg of 1 amu, the atomic unit of mass,
in value and the standard
deviation in sigma (if two output arguments are specified).
The value and the standard deviation are taken from the 2002 CODATA collection of recommended values.
avogadro, barn, bmagn, bohrrad, boltzm, clight, echarge, emass, faraday, gfree, hartree, molgas, nmagn, nmass, planck, pmass, rydberg