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the sign of the d-value. Not all of the signs are printed; the sign is given at least once in each block of
five entries, and can always be found by looking either up or down the column from the value of d in
question. The correction to altitude for additional minutes of Dec is proportional to d and proportional to
the number of additional minutes.
9.9.2. In the previous example, the latitude was 40o , the LHA of the body was 086o, and the Dec was 5o
N. Suppose the Dec had been 5o17' N. The basic figures obtained would be 06o16' Hc and 089o Z as
before, and the true azimuth (Zn) would still be 271o. The Hc of 06o16' is not correct for a Dec of 5o17'
N, but is correct for 5o N. The Hc change for an additional 1o of Dec (d-value) is +39 minutes of altitude.
However, the correction needed in this case is for 17 minutes of Dec, not a whole degree. Consequently,
the additional correction is 17/60 of 39'. To the closest whole number, this would be +11 minutes of
altitude.
AFPAM11-216 1 MARCH 2001 223
Figure 9.6. Enter Tables With Latitude, Declination, and LHA.
9.9.3. This multiplication can be done on the slide rule face of the DR computer or by means of a table
found in back of Pub. No. 249, Volumes 2 and 3. A portion of this table is shown in Figure 9.7. Notice
that there are no signs listed. The proper sign for the answer from this table is the same sign as the basic
d-value. A rule of thumb is the correction will be a plus (+) for declination of same name as latitude and
a negative (-) for declination of contrary name as latitude. Values of d are given across the top of the
table, and additional minutes of Dec are given down the side of the table. In the table, the correction 11'
is found by looking across 17' for Dec and down 39' for d to their intersection at 11'. Since the sign of
the d-value is plus, this correction is added to the tabulated Hc. The correct Hc value then becomes
06o16' + 11' or 06o27'.
9.9.4. Following is a sample problem illustrating the solution. Refer to the portion of the tables in Figure
9.8 for the solution. Suppose the sun is observed at 1005 GMT. The DR position is 38o12' N, 101o47' E,
and the Ho of the sun is 10o52'.
224 AFPAM11-216 1 MARCH 2001
Dec of the Sun for 1000Z S7o37'
GHA Sun for 1000Z 326o53'
Correction to GHA for 5 minutes +1o15
GHA Sun for l005Z 328o08'
Closest longitude for whole degree LHA +E101o52' (assumed longitude)
430o00'
–360o00'
LHA Sun for 1005Z 070o00'
Figure 9.7. Table Performs the Multiplication.
Figure 9.8. Declination 0-14o Contrary Name to Latitude.
9.9.5. The closest whole degree of latitude is 38o N and is used as the assumed latitude. Since the
assumed latitude is north and Dec is south, the navigator must use Pub. 249, Volume 2, page for 38o
latitude which is headed Declination (0o–14o) Contrary Name to Latitude. Following LHA 070o across
the page to 7o Dec, the navigator extracts:
AFPAM11-216 1 MARCH 2001 225
Tab Hc 11o-06'
d-value -40'
Z 108o
d-correction from Pub. No. 249, Volume 2 -25'
Corrected Hc 10o-41'
Zn using rule in the upper left-hand corner of the page 252o
9.10. Postcomp Summary. Before proceeding, review the procedures for finding the Hc and Zn of a
body whose Dec lies between 30o N and 30o S, using Pub. No. 249, Volume 2 or 3.
9.10.1. Shoot the body and record the time of observation, the body's name, and the Ho.
9.10.2. From the Air Almanac, extract GHA and Dec of the body for the time of the observation.
9.10.3. Assume a position close to the DR position so that the latitude is a whole number of degrees and
the longitude combined with the GHA of the body gives a whole number of degrees of LHA of the
body. Find the LHA of the body for this position.
9.10.4. Select the correct volume (2 or 3) and page that contains the correct arguments of Dec and LHA
of the body, temporarily disregarding the odd additional minutes of Dec. Thus, if the Dec were N19o55',
use the column for 19o. Select the table labeled Declination Same Name as Latitude, if Dec and latitude
are both north or both south, or select the table labeled Declination Contrary Name to Latitude, if one is
north and the other south. Opposite the LHA of the body, read the tabulated altitude, d-value, and Zn in
the column headed by the whole degrees of Dec.
9.10.5. If the Dec is not a whole number of degrees, determine the correction for the additional minutes
of Dec. Enter the table in the Pub. No. 249 volume with the value d and the number of additional
minutes of Dec. Apply the correction to the tabulated altitude (Hc) according to the sign of d. This is the
corrected Hc.
9.10.6. Convert azimuth angle (Z) to true azimuth (Zn) by means of the rule at the top or bottom of the
　
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