STATIC PARALLAX CORRECTIONS

are correct only for equipment located exactly at the reference point. Dynamic differences result because the motion of equipment not located at the reference point is different from the motion of equipment located at the reference point because of the rolling and pitching of the ship. These dynamic factors are usually negligible and are not normally corrected. STATIC PARALLAX CORRECTIONS.— Static parallax is caused by the linear and angular dis- ment located elsewhere on the ship. Figure 3-5 shows two parallel reference frames (X and Y) displaced from each other by the distance (d). Frame X is the standard reference frame. The bearing of target (T), as determined from reference frame X, is 60°. If this is applied in a reference frame at Y, the line YT is deter- mined. This line is parallel to XT, but it does not pass through the target because of the displacement be- tween the reference frames. To cause the line from Y to pass through the target in this example, a parallax correction angle of 10° must be subtracted from the placements between the reference point and the equip- bearing value measured for frame X. Figure 3-5.—Parallax resulting from linear displacement of two frames. 3-4