its 0.1% to HQ find per 1 perception, so the +10 armlet gives a 1% increase
Every item has its own HQ find % per your lvl like gathering grade 1 at lvl 50 might give you 25% hq find per item and gathering grade 5 item at lvl 50 would be only 5% HQ find

Just get to the max available 170+ and have a +17% hq find...
hope that helps
Stat increase on quality and double down are the same. every 1 = 0.1%