A large number of applications exists for measuring the resistivity or other properties of ferrous and nonferrous metals, including matching alloys to ensure weld compatibility and measuring weld size to estimate weld strength. In the present invention, a DC current-reversal technique allows for accurate electrical measurement with a 4-point probe, alleviating problems due to surface potentials, thermal effects, and eddy currents that previously rendered such measurements inaccurate. Estimates of thermal conductivity, flaw size and location, among others, can also be obtained.