The factual accuracy of this diagram or the file name is disputed.
Reason: The dip angle is designated here as the angle between the dipe line of the „real“ (i.e. the red/pink) plane and the East direction. Since the real plane does not strike in N-S direction, there has to be a dip direction line within the horizontal plane which is oriented 90° to the strike line and not identical to the East direction. The dip angle then is the angle between the dip direction line of the horizontal plane and the dip line of the „real“ plane. See this image.
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