Not to be too silly about it, but...
I always take a compass with me when I go out to tweak a dish.
I didn't the other day, relying on relative offset from some other dish on the roof, and found squat.
Next day, I took my 10¢ compass and was on the bird in seconds.
Well, I do cheat.... by lining up an 18" level with the compass, then using the level as a pointer.