Item stat variance (drops)

For primary stats and auxiliary stats (accuracy, avoid, speed, jump, etc) , it should be what Cyanne said (floor(avg/10) + 1) and an extra 1 for gach. For weapon and magic attack, it's ±7 or 8 even with normal drops (not gachapon or boss specific), same applies for weapon/magic defense. HP/MP seems to be ±5. There is probably a general formula and a cap so I'm most likely working on the cap here in regards to weapon/magic att; lower attack base weapon may have less variance.