turbines may be selected for analysis of the angle of attack these may be the ones having the worst measured vibration in this way the analysis can be applied only to those having a vibration beyond a predetermined set value to avoid analyzing all of the blades of all of the rotors fig1 shows a symbolized view in a picture taken to assess blade angles deviation thereof or absolute angles of attack thereof a deviation between each blade can be described with a positive or negative angle the direction u201c u201d or u201c u2212 u201d may vary and might be specified in the pitch control system the same angles cannot only be used for comparison to each blade but also in reference to an objects which has a known geometric alignment to the rotor plane to determine the absolute angle of attack those objects are usually part of the nacelle 11 or a visible piece of main shaft 9 while the camera c is standing still the objects in fig1 will not be at identical positions during a set of pictures within the picture due to movement of the turbines tower and head section and therefore the use of the outer limits of the picture frame have proven to be insufficient as reference for angle measurements fig2 shows the general setup for a camera to go through the calibration process the camera c is mounted on a suitable mount like a tri pod t and is lined up with the optical axis to the center of a grid made g of squares both the.