change ratio of a quantity

https://doi.org/10.1351/goldbook.C00969
A term which may be expressed infinitesimally at time t by a ratio of differentials dQ1(t)dQ2(t) where the kind of quantities are the same but for different components in the same system. In practice, the ratio for a finite interval is: ΔQ1(t1;t2)ΔQ2(t1;t2) Examples are: mass change ratio, dm1(t)dm2(t);
amount of substance
change ratio, dn1(t)dn2(t).
Source:
PAC, 1992, 64, 1569. (Quantities and units for metabolic processes as a function of time (IUPAC Recommendations 1992)) on page 1571 [Terms] [Paper]