NavList:

In flight navigation you apply the sextant corrections to the computed altitude to create Hp, "precomputed altitude." This then allows you to compare your raw sextant altitude to the Hp to obtain the intercept which is much quicker than the marine practice of making the corrections to the Hs after the shot to obtain Ho after the shot is taken. You apply the corrections to the Hc with the sign reversed from the marine practice.

Let's say that the Hc is 40° 15' and the Hs is 40°  35' and the index error (IE)  is +6' (on the arc) and the height of eye is 16 feet.  [IC is IE with the sign reversed.]

Marine method            flight method

Hs  40°   35'                    Hc    40°   15'

IC        -  6                     IE            + 6

DIP       -4                      DIP          +4

REF     -  1                     REF         +1

--------------------                 ---------------------

Ho    40°   24'                   Hp     40°   26'

Hc    40°   15'                   Hs     40°   35'

----------------                     ---------------------------

INT         9 T                   INT         9 T

You get the same intercept either way. 

So, when making a graph for precomputations you draw in the curve of Hp with all the sextant corrections already applied and compare the raw Hs with the graph.

The only criticism is that the refraction correction is actually based on Ha not Hc so the correction taken from the table might fall on one side of the correct value or the other, but this is not a problem in real life. A difference of 0.1' from the Nautical Almanac refraction table of 1' from the Air Almanac table had no real consequence in the real world.  

In fact, just memorize the refraction corrections to the nearest one minute, 5' above 10°  ; 4' above 12°  ; 3' above 16 ; 2' above 21°  ; 1' above 33°  and 0' above 63°. And for the dip correction just do the square root in your head, 2' for 4 feet; 3' for 9 feet; 4' for 16 feet; 5' for 25 feet, etc.