It's probably an old discussion, but I still dont have this clear in my head
Of course we all know that using an artificial horizon doubles the actual elevation of a body which at some point requires division by two.
The worksheets show that when taking a shot with an artificial horizon one must add or subtract index error to hs before dividing.
Im sorry but this needs explaining. Because index error is like a constant it does not change with elevation so why add it to hs before an AH division? The index error is then halved. Seems to me all corrections to hs should be made after division, that means altitude correction and index error.
Stupid me just doesnt see how index error can double just because the height is doubled while using an AH.
Lets just say your index error is 20 degrees on the arc and the AH elevation is 60 degrees. So according to the work sheet you subtract 20 from 60 then divide by 2 which equals 20 degrees elevation. Dividing first then subtracting index error equals 10 degrees elevation. You can see there is a difference although index error is not likely to be this bad.
I dont currently have any ie in my sextant so it's difficult to experiment. Someone with two sextants, one way off, might have an opportunity to check out the math with observations.
Cheers
Of course we all know that using an artificial horizon doubles the actual elevation of a body which at some point requires division by two.
The worksheets show that when taking a shot with an artificial horizon one must add or subtract index error to hs before dividing.
Im sorry but this needs explaining. Because index error is like a constant it does not change with elevation so why add it to hs before an AH division? The index error is then halved. Seems to me all corrections to hs should be made after division, that means altitude correction and index error.
Stupid me just doesnt see how index error can double just because the height is doubled while using an AH.
Lets just say your index error is 20 degrees on the arc and the AH elevation is 60 degrees. So according to the work sheet you subtract 20 from 60 then divide by 2 which equals 20 degrees elevation. Dividing first then subtracting index error equals 10 degrees elevation. You can see there is a difference although index error is not likely to be this bad.
I dont currently have any ie in my sextant so it's difficult to experiment. Someone with two sextants, one way off, might have an opportunity to check out the math with observations.
Cheers