Accuracy of measurements of the quantized Hall resistivity by a direct current comparator type potentiometer

In this paper the accuracy of measurements of the quantized Hall resistivity (QHR) by a direct current comparator type (DCC) potentiometer is estimated based on a linearity calibration of the potentiometer using a Josephson potentiometer. The power coefficient contribution to the nonlinearity of the DCC potentiometer is found to be 0.15 +- 0.02 ppm/(100 mV)2 at 18.5 +-0.50C in 1985 and 0.21 +- 0.03 ppm/ (100 mV)2 at 20.5 +-0.50C in 1988. The possibility of accurate measurements of the ratio QHR/Rstd with uncertainties less than 0.05 ppm by the DCC potentiometer is discussed