At 17:01 +0000 02/09/4, Barbara and/or Bill Hooper wrote:
SI is a system of UNITS not a system of QUANTITIES. Length is a quantity;
meter is its SI unit. Refractive index is a quantity; it is unitless (in any
system of units).
Taken from the book "International vocabulary of basic and
general terms in Metrology", BIPM/ISO 1993:
1.1 (measurable) quantity. Attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined quantitatively.
1.2 system of quantities. Set of quantities, in the general sense, among which defined relationships exist.
1.3 base quantity. One of the quantities that, in a system of quantities, are conventionally accepted as functionally independent of one another.
1.7 unit (of measurement). Particular quantity, defined and adopted by convention, with which other quantities of the same kind are compared in order to express their magnitudes relative to that quantity.
1.9 system of units (of measurement). Set of base units, together with derived units, defined in accordance with given rules, for a given system of quantities.
Does that help?
Louis
