Every planet has a specific degree at which it is exalted. It is debilitated at the degree 180 degrees opposite that point. The closer it is to the exaltation point, the more exalted it is, the closer to the debilitation point, the more debilitated. For the purpose of assessing exaltation, the borders of signs are irrelevant.
Exaltation itself (and debilitation) is a confusing principle, as to when it should be considered and what it effects. It is NOT actually a principle of dignity, it is a principle of potency. Nevertheless potency and dignity are somewhat interrelated. However, it is safe to say that one should consider dignity by vargavimshopaka (an evaluation that includes many zodiac subdivisions and ignores debilitation and exaltation), and one should consider potency by sad-bala, which automatically takes exaltation and debilitation into account. On top of this, one should just keep a special eye towards exaltation and debilitation effects, but not in a context that makes them all-important independent from vargavimshopaka dignity and shad-bala potency.
– Vic DiCara