The invention relates to a method for pitch angle measurement and/or for constructing a pitch angle measurement system on a rotor blade (100) of a wind turbine, the rotor blade comprising a blade root (114) and extending along a longitudinal blade axis (180). The rotor blade is rotatably mounted, by its blade root (114), to rotate about the longitudinal blade axis (180), on a rotor hub (20) of the wind turbine, the rotor hub rotating or being rotatable about a rotor axis (36). At least one chord line direction indicator (430) is firmly connected to the rotor blade (100) at a distance from the blade root (114), and defines a chord line direction indicator direction (160) indicative of a direction of a chord line (140) of the rotor blade (100) at the location of the chord line direction indicator (430). The rotor blade (100), or at least one rotor blade portion (101) of the rotor blade firmly connected to the chord line direction indicator (430), is produced in a mould (200) before being connected to the chord
