Comparison of Zener voltage standard calibrations at 10 V between the KRISS and the ETL

In order to promote the improvement of the KRISS´ 10 V calibration system a comparison of 10 V dc voltage calibrations between the Korea Research Institute of Standards and Science (KRISS, Korea) and the Electrotechnical Laboratory (ETL, Japan) was conducted from Sept.-Oct. 1995. A commercial Zener voltage standard was carried for the comparison. During the comparison an unexpected discrepancy was found and its origin was experimentally traced to find a correction value. After the correction was made, the result showed the two 10 V calibration systems, both of which are based on 10:1 divider and 1 V Josephson array were in a good agreement within an uncertainty or the comparison which was less than 0.1×10^-6. Uncertainty of the KRISS system has been improved to be 0.022×10^-6