The electrical resistivity rho of a metal can be expressed as rho = rho _I+ rho _T+ rho _CW+ rho _GB where rho _I and rho _T are the components of the resistivity due to impurities and lattice vibrations respectively. rho _CW is the component of the resistivity due to cold work while rho _GB is that due to grain boundaries. Both rho _CW and rho _GB will change on annealing. rho _CW will be reduced as the imperfections anneal and rho _GB will decrease with grain growth. Unfortunately these effects are usually masked by changes in rho _T except under high stability isothermal annealing conditions. The technique described represents a novel method of suppressing rho _T and allows direct measurement of rho _CW+ rho _GB. This makes possible the in situ monitoring of industrial annealing processes.