ABSTRACT
This chapter describes the historical development of the voltage standard and the properties of the version of the Josephson voltage standard at present in use. The 200 year history of standard cells abruptly ended with the introduction of quantum standards based on the Josephson effect which reduces the calibration of a d.c. voltage to the determination of a frequency and the knowledge of the ratio of twice the elementary charge and Planck’s constant 2e/h = (Φ
( Josephson 1962). As the frequency is finally controlled with extreme accuracy by the standard atomic caesium clock, only a convention on the value of Φ
for the voltage calibration than was obtained before with electrochemical cells. Moreover, complicated international comparisons for the adaptation of voltage standards were no longer required.
