ESTABLISHMENT OF BENCHMARK AND TRAM REFERENCE READINGS

The two types of train and elevation zero align- ment are equipment with alignment or boresight tele- scopes and equipment without telescopes. Equipment with alignment or boresight tele- scopes: Train zero is defined as the angle at which the telescope axis is parallel to the ship’s centerline plane. Elevation zero is that angle at which the telescope axis is parallel to the RPP. Train and elevation zero align- ment is carried out by physically positioning each equipment to train and elevation zero by using sur- veying techniques and zeroing the dials and synchros, or by compensating for the train and elevation errors through computer software changes.’ Equipment without telescopes: Train and elevation zero alignment is accomplished by matching an indicator to a scribe mark or plate and zeroing the dials and synchros. PERFORMANCE OF TRAIN AND ELEVATION SPACE ALIGNMENT (STAR CHECKS) The sixth major step of initial alignment is train and elevation alignment between the alignment reference and other combat systems equipment. This is accomplished by comparing equipment position when the optical axes are made parallel by sighting on a celestial body. If the train and elevation readouts for the equipment do not agree within the operational tolerances previously established for that equipment, alignment is necessary. After corrective alignment is accomplished, a new set of tram or benchmark read- ings must be taken and recorded. This alignment check can be performed by a ship’s force or a support activity. ESTABLISHMENT OF BENCHMARK AND TRAM REFERENCE READINGS The seventh and last major alignment step is the establishment of reference readings that are performed by a support activity or a ship’s force. Reference read- ings are established to furnish an easy means of checking train and elevation alignment in the future. This is necessary because the dials or synchros may become misaligned as a result of vibration and normal wear or equipment disassembly for the replacement of worn parts. Tram and benchmarks are provided to facilitate checking combat systems equipment at a definite train and elevation position. The position selected may be any convenient value within the limits of the equip- ment movement. The dial readings for these positions are recorded on the sheets provided in the alignment smooth log. If the equipment remains aligned cor- rectly for zero train and elevation, the recorded dial readings are the same whenever the equipment is moved to the tram or benchmark position. The alignment verification obtained by using a benchmark is accurate only if the angle between the reference line and the position of the pointing line established by the benchmark does not change as a result of hull distortion or some other cause. Adjust- ments to equipment should not be made by using the result of a single benchmark check. Instead, bench- mark results should be recorded each time they are performed so that a determination can be made when a benchmark error begins repeating itself and becomes an indication that further alignment checks are re- quired. Tram bars and tram blocks may also be used to establish an angle by determining a definite distance between a point on the rotating structure of the equip- ment and a point on its fixed structure. An error, as defined by tram readings, may also result if the fixed structure shifts on its mounting. Any adjustments to equipment, like benchmarks, should not be made on the basis of a single tram check. Some equipments have both benchmarks and trams. When the benchmark reading changes and the tram reading remains unchanged, the extent of hull distortion is revealed. 3-15