The increment of the value of a quantity \(Q\) with time. The change may be expressed either infinitesimally at time \(t\) by the differential \(\text{d}Q\) or \(\text{d}Q(t)\), or in practice it may be expressed by a finite increment over the time interval \((t_{1};t_{2})\), i.e. \(Q(t_{2})- Q(t_{1})\), which may be written \(\Delta Q\) or \(\Delta Q(t_{1};t_{2})\) \[\Delta Q = \Delta Q(t_{1};t_{2}) = Q(t_{2})- Q(t_{1})\] Examples are: mass change, \(\Delta m\); @A00297@ change, \(\Delta n\); volume change, \(\Delta V\); @S06072@ change, \(\Delta c\).