are correct only for equipment located exactly at thereference point. Dynamic differences result becausethe motion of equipment not located at the referencepoint is different from the motion of equipmentlocated at the reference point because of the rollingand pitching of the ship. These dynamic factors areusually 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 showstwo parallel reference frames (X and Y) displacedfrom each other by the distance (d). Frame X is thestandard reference frame. The bearing of target (T), asdetermined from reference frame X, is 60°. If this isapplied in a reference frame at Y, the line YT is deter-mined. This line is parallel to XT, but it does not passthrough the target because of the displacement be-tween the reference frames. To cause the line from Yto pass through the target in this example, a parallaxcorrection angle of 10° must be subtracted from theplacements 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
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