Ability check modifier bonueses from items

[drack]

Say, I was wondering if anyone has the formula for ability check bonuses like the +3 bonus that a circuit of persuasion gives. http://www.dandwiki.com/wiki/SRD:Circlet_of_Persuasion I remember reverse calculating it once, but I put it somewhere and forgot it. Thanks in advance. :smallbiggrin:

[Namfuak]

Based on that particular item, for purchase they are worth 1500 per +1, and for crafting 750. This would be for a competence bonus, of course, any bonus that stacks with other bonuses of the same type (or untyped bonuses) would be more expensive.