>>3002990go to your key items and then your user guide. it has a qualities page that details all the things the qualities do, which is: stat gains and resale modifiers. the stats listed there are how much the weapon/armor will gain when you dualize it with a shard of that quality.
when dualizing weapon/armor and shards, or two tempered equips, the resulting quality is always the lower (less letter) one, EXCEPT when both have the same number of letters, in which case it gets upgraded to a higher amount of letters. not sure how to determine which higher word you get, though.
for example: worthless, when tempered onto a weapon will give 1 of p.atk/c.atk/acc. when pointless is tempered onto a weapon, it will get 10 of all those stats.
i hope that helped.