Reciprocal of @R05316@. This quantity is a tensor in an anisotropic medium. It was formerly called @S05797@.
Sources: Green Book, 2nd ed., p. 15 [Terms] [Book] PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 967 [Terms] [Paper]