A wind turbine rotor includes a hub with a rotor blade mounted to a bearing of the hub wherein the rotor blade has a longitudinal axis extending in a radial direction relative to an axis of rotation of the hub, and the rotor blade is rotatable about its longitudinal axis whereby the pitch of the rotor blade is adjustable. The rotor blade has a tag such as an RFID tag fixed on the rotor blade at a predetermined angular position about the longitudinal axis of the rotor blade; and a sensor is fixed on the hub for contactless sensing of the tag when the tag is in a predetermined angular position about the longitudinal axis of the rotor blade. Repeated and accurate calibration of rotor blade pitch is hereby made possible.