Abstract: A method for performing a plurality of measurements in the air gap between a stator and a rotor of a generator for a wind turbine is provided The method steps include: mounting distance measuring sensors on a surface of the stator and/or the rotor, the surface facing the air gap, each distance measuring sensor distanced from the other distance measuring sensor(s) along rotational axis, rotating the rotor about the rotational axis, while rotating the rotor, measuring distances between the distance measuring sensors and respective facing points across the air gap, deriving from the distances one or more value(s) of one or more parameter(s) associated with the air gap and/or the stator and/or rotor, wherein a portion of distance measuring sensors are fixed to a longitudinal support, the longitudinal support being fixed on a surface of the stator and/or the rotor, the surface facing the air gap, during the step of mounting.