10 USE OF THE TABLES 
18. The difference in the azimuth of the heavenly body due to the adoption 
of an assumed position differing from the D. R. position may be neglected for 
nearly all practical cases. However, when high altitudes are observed within 
an hour of the meridian the correct azimuth can be obtained only by using the 
data for a point at or near the observer’s position. Therefore, under these 
conditions the assuming of a position to fit the tables may produce an appreciable 
error in the azimuth, with consequent deflection of the line of position. This 
source of error may be avoided by interpolating to minutes of latitude within 
Table I. 
19. A study of azimuth tables shows that rapid changes of azimuth occur 
within an hour of the meridian, and this, coupled with difficulties of observation, 
makes such azimuths of little value in the accurate determination of compass 
error. The most favorable time for the determination of compass error is when 
the heavenly body is low and near the prime vertical (when the body bears to 
the eastward or westward.) 
USE OF THE TABLES 
ALTITUDE AND AZIMUTH 
(Case I (L. H. A. less than 90°; d+6 less than 90°).—For the sake of brevity, 
the corrected observed altitude will be given in each case instead of the sextant 
altitude, index correction, and height of eye. 
Problem 1—The U.S. S. Richmond is making passage from the United States 
to Montevideo. At about 1650, on March 26, 1928, she was in D. R. position 
latitude 31° 047 S., longitude 49° 35:7 W. At this time the sun was observed 
as follows: Watch 45 52™ 27s; C-W. 25 47™ 17s; chronometer slow 12™ 28»; 
corrected observed altitude 18° 16/5. Required the line of position. 
h m 8 
Wer aee. see a 4 52 27 
CHW ote. 2 Se. 2 47 17 
19 389 44 
Cee. Ca is a5 
G. C. T. 26 Mar. 19 52 12 
Ba: tk. os Es (—) 5 411 
CR. Bee eee eee 19 46 30.9 
Subtract 12 
2a: Fey, Ge eee 7 46 30.9 W. 
neiss. ae cy See HG? 377" W. 
Ass. dong. .==- (—) 49 37.7 W. 
——_————_——_ (Assume a longitude such that the 
bad An 3232. 67 W. __ resultant L. H. A. will be an integral 
degree.) 
Enter Table I with t=67°, L=31°, and on page 37 pick 
out for these values the value of b, A, C, and Z’. Com- 
>| bine the value of b thus found with the declination 
a ee 67" obtained from the Nautical Almanac to obtain d+. 
7 ote tee (b takes the same sign as the latitude; d and b are added 
degree:) when the signs are alike; subtracted when the signs are 
e unlike.) With the value d+b thus obtained enter 
Table II and pick out the corresponding values of 
Band D. These will be found on page 55. 
