On aspects of calibration of DC resistance ratio bridges

In many NMIs and calibration labs are widely used automated dc resistance ratio bridges (RRBs) for resistance and thermometry calibration purposes. Their stated relative accuracy for ratio measurements is for most accurate devices on the level up to 2×10
^-8
. Calibration of such devices and their use place demands on operators to carefully fulfill operation conditions not only for RRB, but for used reference resistance standards too. This paper describes observations achieved during investigation of calibration of RRB.