A metric system of units devised by A. Giorgi (and sometimes known as Giorgi units) in 1901. It is based on the metre, kilogram, and second and grew from the earlier c.g.s. units. The electrical unit chosen to augment these three basic units was the ampere and the permeability of space (magnetic constant) was taken as 10−7 H m−1. To simplify electromagnetic calculations the magnetic constant was later changed to 4π × 10−7 H m−1 to give the rationalized MKSA system. This system, with some modifications, formed the basis of SI units, now used in most scientific work.