Each Josephson voltage standard system supplied by Supracon AG is measured directly against the primary Josephson voltage standard system certified by the Physikalisch-Technische Bundesanstalt (PTB) at a voltage of 10 volts. This ensures that the system’s functionality and highest possible accuracy are reliably verified. Regarding the deviation of the measured value from the actual nominal value of 10 V, results with a near-certain probability of only 1 nV deviation are achieved — a minimal variance attributable to the noise of the null detector.