Looking at Hayate's and Nanoha's spells, some of them are given a rank. For instance, Nanoha's Starlight Breaker is ranked S along with Blast Calamity and Hayate's Ragnarok, while Hayate's (or Reinforce's to be exact) Diabolic Emission is ranked S-
While there is information on Ranks, these seem to only refer to the TSAB's internal Mage Ranking and not how they relate to spells.
I am wondering if the Spell Ranks have any numerical equivalent to them – something similar to The Nasuverse Rankings (in which B = 40, A = 50, and the power after appending +'s is (Rank Value + (Rank Value x No. of +'s)), so A++ = 150).