The SD is to be added to the observed altitude in case the lower limb is brought in contact with the horizon, and subtracted if the upper limb is used. Probably most of the sights you take will be of the sun's lower limb, i.e., when the lower limb is brought in contact with the horizon, so all you need to remember is that in that event the SD is additive.
Now at first we will correct altitudes by applying each correction separately, but as soon as you get the idea, there is a short way to apply all four corrections at once. This is done in Table 46. However, disregard that for the moment. Put this in your Note-Book:
| Dip is -. | Table 14 Bowditch |
| Refraction is -. | Table 20 Bowditch |
| Parallax is +. | Table 16 Bowditch |
| S.D. is +. | Nautical Almanac |
Observed altitude of Sun's lower limb is expressed
.
True altitude is expressed
.