The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
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Hulk is known for his UNPREDICTABLE tactics, I don't know where you came to that ridiculous conclusion, proves to me you don't know the Hulk character very well.
The problem with that is, Hulk ALWAYS holds back against EVERYONE he's fighting, due to the fact he doesn't want to destroy the Earth, Solar System, Galaxy, or Universe because there are innocent lives, therefore that renders your argument useless, Thor has never undermined or overestimated his abilities over Hulk every time they've thought, Thor has given it his all, while Hulk was at a low or a mid-level of rage, because he is far more powerful and fast than Thor ever was, feats prove as much, this was confirmed during Heart Of The Monster, a fantastic Hulk Graphic Novel which explains his character quite well, I sincerely suggest reading it, you may have a better understanding of Hulk.