The time derivative \(\frac{\text{d}Q}{\text{d}t}\) of the value of the quantity. The differential quotient may also be called derivative (or instantaneous) rate of change. Examples are: rate of change of mass, \(\frac{\text{d}m}{\text{d}t}\); rate of change of @A00297@, \(\frac{\text{d}n}{\text{d}t}\).