Preparing for the new volt and ohm

New representations of the volt and ohm, which are to go into effect on Jan. 1, 1990, are discussed. Based on the Josephson and quantum Hall effects, these new representations will change the values of present-day volt and ohm representations and, by derivation, those of the ampere and watt. The new standards will eliminate the differences that currently exist among the volt and ohm representations of different countries. The quantum Hall-effect standard will eliminate the time variation, or drift, of any national ohm representations that are based (as most are) on wirewound resistors, which age. The new representations will also be highly consistent with the volt and ohm as defined in the International System of Units. Classes of standards and instruments that will be affected are identified, and examples of specific reference standard and instrument adjustments that must be made at the start of 1990 are provided.>