The following steps are performed in order to test a tap changer (20) of a transformer (5; 6) which tap changer is designed to change a transmission ratio of the transformer (5; 6):generating a test signal which is supplied to a winding (1-3; 10) of the transformer (5; 6) and to the tap changer (20).Repeatedly actuating the tap changer (20) in order to change the transmission ratio with each actuation.Determining a curve of an electrical measurement variable (I; I1; I2) of the transformer (5; 6) over time (t) respectively during the step of actuating the tap changer (20) depending on the test signal.automatically illustrating the curves (41, 42) in a temporally-superimposed manner.