Add red lines from the left corner at 75, 60, 45, 30, and 15 degrees off horizontal. Note that the steepest one, at left, is an axis around which the dragon’s tail oscillates. The vertical dropped from the top of the 60-degree line passes through the right corner of the square-planned tower in the middle ground. Crucially, the vertical dropped from the top of the 30-degree line passes through the point where the lance intersects its crosspiece.