Concerning Mahou Shoujo Lyrical Nanoha's magic...

[Crescent Pulsar S]

If I remember correctly, Nanoha was an A-rank mage at the beginning, right? Later on, when she's much older, she's beyond the A ranks altogether. How does that work? Does the linker core develop more with age, use, or both? Or had she been an S+-ranked mage the entire time, and it took training to make use of her full potential?

I know that mage ranks can be raised via examination, but that didn't seem applicable until StrikerS. I didn't see or hear of Nanoha taking any examinations for her rank in the first and second seasons, which both seemed to be based on mana capacity. (I believe both Nanoha and Fate's mana was measured numerically at one point, and -- if I remember correctly -- they were both over a million.)

So, yeah... I'm a bit confused.

[Pale Wolf]

AAA, technically.

And Nanoha mage rankings are not raw indicators of power. They're generally indicators of 'how insane a task can we trust you with?' Or in alternate parlance, 'how badass are you?' Chrono, for instance, is explicitly noted as having lower mana stats than either of the girls. His ranking in S1/2? AAA+. Higher than either of them, and he whipped Fate hard when they sparred for her AAA ranking exam.

The power is, as you noted, simply measured in pure numbers.

In the early seasons, Nanoha probably didn't have an official ranking - the AAA was a vague ballpark estimate of 'hm, she looks to be around there'. Mana capacity was part of it, but the estimation was from their performance in a fight, not solely power numbers.

Nanoha's mana capacity may have altered somewhat (whether or not linker cores can be exercised or grow is unknown - it may have even lowered due to her various injuries). But she achieved the S+ ranking not because she pumped out more juice, but because she learned better use of what she already had.

Superiour magical control, and better tactical sense. That's the difference between S+ Nanoha and AAA Nanoha. (And whatever her beginning ranking would have been. AAA was end-of-season, and she improved rapidly to get there)

[Spica75]

The rating seems to be sometimes looking at raw power only and other times at a composite of power, skill and some degree of rank testing.

which both seemed to be based on mana capacity.

Power AND skill.
Dont forget that Nanoha ran a training regime that just about anyone else would call insane.

Basically i would say that her raw power started out high, and as she learned to use it, her rating goes up.