ALIGNMENT EQUIPMENT

Elevation angles also are affected by displace- ments between reference frames. If elevation angles measured in one frame are to be used in another frame, they must first be corrected for parallax. The magnitudes of parallax corrections in train and eleva- tion vary considerably with target bearing, elevation, and range, and the magnitude and orientation of the distance between the reference frames. The basic point to remember is that whenever two reference frames are displaced from each other, data measured from one frame is, in general, not equal to data measured from the other frame. If the differences are significant, data measured in one frame must be corrected for parallax before it is applied in other frames. Angular Displacement Connections arising from reference directions or reference planes not being parallel are called rota- tional corrections. If the reference lines are both in a plane that is perpendicular to both reference planes, but the reference planes are not parallel, the bearing angles and the elevation angles are different. When the angle between the reference planes is relatively small, the major difference is in the ele- vation angles; the difference in the bearing angles is usually small enough to be ignored. Figure 3-6 shows rotational corrections between unparallel planes. Figure 3-6.—Rotational corrections between unparallel planes. ALIGNMENT EQUIPMENT Alignment equipment is used by shipboard and shipyard personnel to align combat systems elements. Combat systems alignment checks and adjustments are usually accomplished with tools and test equip- ment normally found aboard ship. Because of required combat systems accuracy, special-purpose instruments are sometimes required for adjustments. This section briefly describes the most commonly used alignment equipment, such as transits, theod- 3-5