The Bureau International des Poids ct Measures (BIPM) carries out a number
of comparisons of de voltage standards with National Metrology Institutes (
NMIs). These take the form of on-site comparisons of Josephson standards or
bilateral comparisons using traveling standards based on Zener diodes. Thi
s paper describes some of the new procedures used in both types of comparis
on and presents some results of five recent BIPM key comparisons.