the thickness can be determined a 1 error in the thickness measured e g with a micrometer corresponding to only 0 3 mil will produce a 1 error in the apparent resistivity surface texturing may make the apparent thickness of the sheet greater than that of the effective thickness resulting in an erroneously large measured resistivity we estimate that the temperature coefficient of the calibration is significantly less than the temperature coefficient of steel which is about 0 3 0 5 u00b0 c the present technique is of sufficient precision for checking sample or lot variations in the resistivity of sheet steels this can provide for example matched alloys to obtain reproducible weld penetrations however the ease and rapidity of the measurement make possible many additional applications to ferrous and nonferrous metallurgy some examples are given below although low carbon low alloy steels have resistivities which substantially depend only on composition more complex steels have a large variation in resistivity with heat treatment resulting for example from the austenitic martensitic transition direct resistivity measurements provide an easy means of testing for the completeness of the transformation the resistivity of silicon transformer steels is an important parameter because of its relationship to eddy current losses the present technique can measure the resistivity without cutting special test coupons in fact resistivity can be measured in the presence of the heavy oxide layer normally present on these steels there is no need to sand off the oxide the resistivities of commercial magnetic alloys permalloy etc vary over a wide range these materials can be easily sorted and distinguished by resistivity measurements many magnetic stainless steels which have similar appearance can be distinguished additionally there are some nominally.