Micri- (unit symbol mc-) is an archaic non-SI decimal metric prefix for 10−14.[1]
It was proposed as a prefix for the CGS-unit of energy, the erg. The micrierg was proposed in 1922 by William Draper Harkins as a unit of energy equating to 10−14 erg,[1][2][3][4][5][6] the equivalent to 10−21 joule, as a convenient unit to measure the surface energy of molecules[5] in surface chemistry.[7] It saw limited use. One electronvolt is about 160 micriergs. In 1991, the micrierg was officially designated the zeptojoule when the zepto- prefix for 10−21 was officially adopted.