The Marine Sextant, Continued
How to Read
Reading a sextant angle involves properly understanding and interpreting
the markings on the arc scale, micrometer drum, and vernier scale.
Follow these steps to properly read a sextant angle:
Locate the position of the index arm mark on the arc scale.
Determine which degrees the mark is between. The lower reading is the
amount of whole degrees.
Locate the position of the zero mark on the vernier scale.
Determine which minutes the zero mark is between on the micrometer drum.
The lower mark is the amount of whole minutes.
On the vernier scale, determine which graduation mark is most nearly in line
with one of the graduation marks on the micrometer drum. This mark
indicates the amount of tenths of a minute.
Note: To make sure you select the correct mark, look at the vernier marks on
each side of the one that appears to be in line with a drum mark. Both
vernier marks will be on the inside of the closest drum marks.
Figure 8-14 is an example of a sextant angle of 67° 40.6'.
Figure 8-14. Reading a sextant angle.