The Automatic Instrument Transformer Test Set (AITTS-98) is used for the measurement of relative errors of Instrument Voltage as well as Instrument Current Transformers. The Test Set reads out the unbalance of a bridge circuit, converts these readings into ratio and phase error values and then presents these values on a LCD screen for the operator. The Test Set is microprocessor controlled and provides very fast measurements (several measurements in a second). To this effect, the instrument can be used to measure and plot the ratio and phase errors while the test voltage or test current are varied slowly over the band of interest. In addition to measuring the ratio and phase errors, the instrument measures the burden connected to the test sample. This feature is very useful when testing Instrument Transformers in the 'installed condition' and the burden is not known.