Abstract: In a method to determine an electrical potential at a predetermined point on a surface of a photoconductor rotating with process speed in an electrophotografic printer, a charge reversal station is arranged at the photoconductor to reverse a charge of the photoconductor. A potential measurement probe is provided adjacent to the photoconductor to measure a potential at the photoconductor. The photoconductor is operated with a speed reduced from the process speed in a ratio of a distance between the charge reversal station and the potential measurement probe and the distance between the charge reversal station and the predetermined point. The potential at the photoconductor is measured via the potential measurement probe which creates a measurement value at the reduced speed. The photoconductor is accelerated to the process speed. The measurement value of the potential measurement probe is used as the electrical potential at the predetermined point.