改写以下段落：The function of transformer ratio is to change the current and voltage transformer ratio of the testing system based on the actual situation of the substation in order to obtain the actual volt

The transformer ratio serves to modify the current and voltage transformer ratio of the testing system in accordance with the prevailing conditions of the substation, thereby enabling the acquisition of precise voltage or current data of the substation. On the other hand, linear adjustment is utilized to fine-tune any minor disparity between the measured value and the displayed value in the traction substation, so as to acquire more precise and reliable data.