DAVIS Mark 15, 25 Sextant - Manual (Page 20)

Page 18
Figure 18
4. Line the two suns up by continuing to move the index arm.
For a lower limb observation, bring the bottom of the mirror image into
coincidence with the top of the image on the liquid.
5. After the observation has been made, apply the index correction.
6. Halve the remaining angle and apply all other corrections (except for
Dip or height of eye correction, which is not applicable) to find the
altitude of the sun.
Note: Since the sextant reading made with an artificial horizon must be
halved, the maximum altitude that you can observe with the artificial hori-
zon is equal to one-half the maximum arc graduation on your sextant.
There may be several hours around noon during which the sun is too high
to take a sextant reading with the artificial horizon, so plan sights for the
morning or evening hours.
OTHER USES for the SEXTANT
Using the Sextant as a Pelorus
A pelorus is used to take bearings relative to your ship’s heading.
1. Pick out three features on the land.
2. With the sextant held horizontally, measure the angle between the
center feature and one of the other features, and note the angle on a
piece of paper.
3. As quickly as you can, measure the angle between the center feature
and the third feature.
4. Lay out the three angles on a piece of tracing paper so that the
angles have a common center point.