Codex of Device Operation (3.5e Equipment)
From D&D Wiki
This item resembles a leather bound book with a small padlock on the side, filled with countless notes, diagrams and drawings that clarify on the usage of magic items and scrolls. When consulted less than one day before using a certain magic device, the codex bestows upon the user a competence bonus to Use Magic Device checks equal to the codex' enhancement bonus. The codex may be used any number of times per day, in relation to any number of different magic items. Consulting the codex about a specific magic item or scroll takes 1d4 minutes of preparation at the start of the day, after which the bonus for the items researched lasts for 24 hours. The codex contains no information on unique magic items.
Prereqs: Craft Wondrous Item, identify. Caster level must be at least equal to the codex' enhancement bonus.
Cost to Create: 800 gp (+2), 3,200 gp (+4), 7,200 gp (+6), 12,800 gp (+8), 20,000 gp (+10).