Reference-volume thermal expansion coefficient (${\alpha }_0=V_0^{-1}dV/dT$)

The derivative $V_0^{-1}dV/dT$ uses a fixed reference volume $V_0$. It differs from the instantaneous fractional coefficient $V^{-1}dV/dT$ by the factor $V/V_0$. The volume convention must be specified before comparing coefficients.