Dish alignment is not at all scientific. This aint astrophysics! (It definitely is astrophysics to the guys that put the bird up there!) The DBS dishes use offset feeds which makes the dish look like it is pointing differently that the RAF beam actually pointing. The markings on the dish are crude, not in any way a precise measurement. They are intended only to get you in the ballpark, as are the Azimuth and Elevation numbers you find on websites, or via your receiver setup menu when you put in your zip code. DBS dishes have quite a wide beam width, so engineering accuracy is needless.
The Installer will simply point the dish approximately in the right direction, both azimuth and elevation. Usually they will get some signal right away. Then using a simple signal strength meter, they will rock the dish back and forth very slowly to peak the signal. Then do the same for the elevation. Then they might go back to azimuth and see if it needs a little more touch-up. Same for elevation. Lock it down and it is in business.
FORGET all about magnetic Variation, Compass Error and Declination. That stuff is needed when installing the larger steerable dishes that need more detailed alignment because they are trying to receive all the satellites in the arc from horizon to horizon, as well as having a much narrower beam width than DBS dishes.
Some receivers have an audible signal strength indicator. With that, you only need to set the receiver and a portable TV outside where you can hear it and rock the dish for the loudest, high pitch tone and you are peaked. That comes in handy if your dish got moved by wind or you have to relocate it.
Now about the Off-Air antenna. As was stated in other posts, those antennas have a very broad beam width. The main reason you would want to be picky about the direction would be to minimize ghosts. This is definitely heavy-duty trial and error as there is no possibility you can determine how signal is going to reflect off trees, buildings, steel structures etc. along the way or near the path to the TV stations. This will usually be somewhat of a compromise, because the direction that gets the clearest signal from one station may exhibit ghosts on others.
Elevation, thankfully, does not come into play here. Moving the antenna from side to side while someone watches the picture and shouts up at you as to when it is best is all that can be done.
There are rare cases when the best picture is had with the antenna pointed AWAY from the TV station. This can be the case when hills, tall buildings or other obstructions shadow you from the station. There are places in the Los Angeles area where huge refinery towers intervene between a location and the TV stations, blocking the signal, but a strong signal can be found reflecting off a refinery tank in an entirely different direction!
Hope this helps, rather than adds confusion.
Tony N
