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From The PSUPedia
Is increased by:
ATA vs ATP
ATA is often lowered on weapons with high ATP, as to balance things out. However, this often changes what weapon choice people use; some people, for example, may go wild for ATA (for example, they are a low accuracy race such as Beast), while others choose power. The argument has been going on since the game's predecessor, Phantasy Star Online; normally, people choose ATA over ATP.
Hit rate formula
You can find the hit rate formula in the Formulae article.