Solving the question of how to manage the antenna elevation knowing distance and difference in altitude (vertical displacement) was the topic of a couple of articles I wrote 17 months ago. As often happens (even IRL!), as we progress into studying and the knowledge broadens, so new solutions to old problems are found.
Although I habitually use the table I generated using trigonometry as it is an immediate and handy solution (it’s always pinned in front of my nose), this article is about a handy formula mentioned in the P-825 R05-02.
A formula to rule them all
The angle is estimated by means of this simple formula:
ElevationAngle = ΔALT / (SR * 100)
Example I
ALTTGT = 15,000ft
ΔALT = 10,000ft
SR = 25 nm
ElevationAngle = ΔALT / (SR * 100) = 4°
Simplification and Example II
As the altitude is pretty much always in thousands of feet, it and the denominator can be simplified: just drop two zeros from the altitude and divide by the SR:
ALTTGT = 15,000ft
ΔALT = 15,000ft
SR = 15 nm
ElevationAngle = 15,0
Verification
For the sake of completeness, these are the values from my model, based on trigonometry. The first example is highlighted in red, the second in green. As you can see, they are quite close.
So, which one should you use? Well, that’s entirely up to you and probably the ones the makes finding the angle faster.
FlyAndWire 
10 degrees for every 10000ft at 10nm. Double if 5nm, half if 20nm.
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That’s a good observation. Another way to put it is dropping three figures at 10nm (so, ten-thousand → ten degrees), then double or half as you suggested. I usually use my table, but this relation at 5nm / 10nm / 20nm is really handy. Thanks!
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