Latitude by Local Apparent Noon (LAN), Continued
The method of taking numerous sights is a modification of the
maximum altitude method. It is useful under conditions where heavy
seas, clouds, and the like may make steady observation impossible.
Well before watch time of LAN, the observer begins taking a series of
altitudes. Their number depends on the difficulties of the situation and
the possible error in computed time of transit. He/she reads off the
altitudes to a recording assistant, turning the tangent screw slightly after
each observation to make sure that the next altitude is an independent
sight. Observations are discontinued when the altitude definitely shows
signs of decreasing.
Under favorable conditions, even a series of skillfully taken observations
may show an occasional erratic deviation from the normal gradual rise
and fall. After sights showing a radical difference from the preceding or
succeeding series are discarded, however, the hang should become
evident, and it should be possible to judge the maximum altitude. The
figure selected will probably be less than the altitude shown in one
observation and more than that below it. The result should give latitude
with an error no more than 1'. This reading is considerably more
accurate than could be obtained by a single sight under the conditions
As you now know, you must first obtain a sight of the Sun when its at
maximum altitude and the time of observation. With this and a DR
position, we can reduce the sight to find latitude; now we can work the
second part of our strip form.