prime ratio
Mathematics (now historical )
noun
(In Newton's theory of fluxions) the ratio of the infinitesimal increments of two variable quantities as they recede from particular values; the rate of change of one variable with respect to another; method of prime and ultimate ratios = doctrine (also method) of limits.
Origin
Early 18th century; earliest use found in John Harris (c1666–1719), writer and lecturer on science. After post-classical Latin prima ratio; compare ultimate ratio.