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: \[\frac{\Delta Q_{1}(t_{1};\,t_{2})}{\Delta Q_{2}(t_{1};t_{2})}\] Examples are: mass change ratio, dm1(t)/dm2(t); amount of substance change ratio, dn1(t)/dn2(t).