It is described a method of determining a quality of an initial value for a blade pitch angle. An initial power captured by a wind turbine is measured, while the blade pitch angle has the initial value. The blade pitch angle is changed from the initial value to a first value in a first direction. A first power captured by the wind turbine is measured and the blade pitch angle is changed to a second value in a second direction being opposite to the first direction. Further, a second power captured by the wind turbine is measured, a power difference between the first power and the second power is calculated, and the quality of the initial value based on the calculated power difference is determined. Further, a control system, a wind turbine and a computer program are described.