The method of calculation is the absolute differential calculus, or tensor analysis, of M. M. G. Ricci (1853–1925, Italian), which was noted earlier in connection with the general progress of recent mathematics toward structure. The Ricci calculus, however, originated in the algebra of quadratic differential forms. […] The Ricci calculus did not come into its own geometrically until it was publicized by the relativists, when the geometers adopted and further developed it.