The Compton wavelength of a particle is equivalent to the wavelength of a photon whose energy is the same as the rest-mass energy of the particle.  The Compton wavelength divided by 2`pi` is useful in quantum mechanics and this constant is known as the 'reduced' Compton wavelength.  This constant is expressed in units of meters.

Notes

This constant is specified with a standard uncertainty (standard deviation) of: 0.00000025 E-15 m