 The NIST scientists devised a method to compensate for silver lost from the anode by mechanical causes , and conducted an isotope analysis of the silver used to determine its atomic weight . Their value for the conventional Faraday constant is F90 = <unk> @.@ 39 ( 13 ) C / mol , which corresponds to a value for the Avogadro constant of 6 @.@ <unk> ( 78 ) × 1023 mol − 1 : both values have a relative standard uncertainty of 1 @.@ 3 × 10 − 6 . 
