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Two determinations of the unit of resistance in terms of mutual inductance and frequency were made during 1951 using Campbell's bridge method. They gave the same value within 1 part per million, and the mean value agreed with that found in 1936 to the same accuracy. The value obtained for the ohm as maintained by the group of coils forming the reference standard at the National Physical Laboratory is: 1 N.P.L. ohm = 1.000002 Â± 0.0000015 absolute ohm.