An improved determination of the ratio of power, measured in terms of the Josephson and quantum Hall effects, and also the meter, kilogram, and second, has been completed. The result is expressed as: W/sub 90//W=1+(8/spl plusmn/87)/spl times/10/sup -9/. This is an order of magnitude improvement from the last NIST (formerly NBS) determination. The Type A relative standard uncertainty (statistical) is 30 nW/W, and the Type B relative standard uncertainty is 82 nW/W. Type B uncertainty components are listed and discussed within the context of experimental procedure descriptions. Improvements for the next version of this experiment are also mentioned.