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10.4.2. In addition, motion corrections may be determined by using a modified MB-4 computer. This
modification allows for greater accuracy and speed in computation of combined motions (motion of the
observer and motion of the body) than the Pub. No. 249 tables. For a discussion of this modification, see
Chapter 12.
10.5. Special Celestial Techniques. The main difference between the basic methods of precomputation
is the manner in which the motion of the observer and the motion of the body corrections are applied. In
the graphic method, both corrections are applied graphically by movement of the assumed position or
the LOP. In the mathematical method, both corrections are applied mathematically to the Hc, the Hs, or
the intercept after being obtained from tables, a modified MB-4 computer, or the Pub. No. 249.
10.6. Celestial Computation Sheets. The format in Figure 10.2 is a typical celestial precomputation and
illustrates one acceptable method of completing a precomputation. The explanation is numbered to help
locate the various blocks on the celestial sheets (Figure 10.2). NOTE: Not all blocks apply on every
precomputation.
AFPAM11-216 1 MARCH 2001 231
Figure 10.1. Correction for Motion of the Body.
232 AFPAM11-216 1 MARCH 2001
Figure 10.2. Typical Celestial Precomputation Format.
AFPAM11-216 1 MARCH 2001 233
1. DATE. Place the Zulu date of the Air Almanac page used in this block.
2. FIX TIME. GMT (coordinated universal time) of the computation.
3. BODY. The celestial body being observed.
4. DR LAT LONG. The DR position for the time of the observation.
5. GHA. The value of GHA extracted from Air Almanac (10-minute intervals).
6. CORR. The GHA correction for additional minutes of time added to the GHA in block 5 and, if
necessary, the 360o addition required establishing the LHA. SHA-When a star is precomped with
Volume 2 or 3, SHA is placed in this block.
7. GHA. Corrected GHA (sum of blocks 5 and 6).
8. ASSUM LONG (-W/+E). The assumed longitude required to obtain a whole degree of LHA.
9. LHA. LHA of the body (or Aries).
10. ASSUME LAT. The whole degree of latitude nearest the DR position.
11. DEC. The declination of the celestial body (not used with Volume 1).
12. TAB Hc. The Hc from the appropriate page of Volume 2 or 3.
13. D. The d correction factor found with previous Hc. Include + or -, as appropriate. The value is used
to interpolate between whole degrees of Dec.
14. DEC. Minutes of declination from block 11.
15. CORR. The correction from the Correction to Tabulated Altitude for Minutes of Declination table in
Volume 2 or 3, using blocks 13 and 14 for entering arguments.
16. CORR Hc. This is the corrected Hc—sum of blocks 12 and 15 or extracted from Volume 1.
17. Zn. True azimuth of the celestial body from the formula in Volume 2 or 3, or directly from Volume
1.
18. TRACK. The true course (track) of the aircraft.
19. GS. The groundspeed of the aircraft.
20. ALT MSL. Aircraft altitude.
21. CORIOLIS. The Coriolis correction extracted from Pub. No. 249, the Air Almanac, or a
Coriolis/rhumb line table.
22. PREC/NUT. Precession and nutation correction computed from the table in Volume 1.
23. REL Zn or Zn. The difference between Zn and track, used to determine motion of the observer
correction.
24. MOTION OF OBSERVER (MOO). Motion of the observer correction for either 1 minute (using 1-
minute motion correction table) or 4 minutes (using 4-minute correction table in Pub. No. 249) of time.
25. MOTION OF BODY (MOB). Motion of the body correction for either 1 minute (using 1-minute
motion correction table) or 4 minutes (using tabulated Hc change for 1o of LHA or 4-minutes correction
table in Pub. No. 249) of time.
26. 4-MINUTE ADJUST. Algebraic sum of 24 and 25; for use of 4-minute motion corrections extracted
from Pub. No. 249.
27. X-Time. Time in minutes between planned shot time and fix time.
28. TOTAL MOT ADJUST/ADV/RET. Correction based on combined motion of observer and body,
for the difference between the time of the shot and fix time. The sign of this correction will be the same
as the sign in block 26 if the observation was taken prior to the computation time. If it was taken later,
the sign will be reversed.
29. REFR. Correction for atmospheric refraction.
30. PERS/SEXT. Sextant correction or personal error.
31. SD. Semidiameter correction for Sun or Moon.
32. PA. Parallax correction for Moon observation.
33. POLARIS/Q CORR. The Q correction for the time of the Polaris observation (extracted from Pub.
No. 249 or the Air Almanac).
234 AFPAM11-216 1 MARCH 2001
34. Total ADJ. Algebraic sum of blocks 28-33 as applicable.
35. OFF-TIME MOTION. Motion adjustment for observation other than at planned time.
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