Tome of the Wyrm

Favored by spellcasters who hunt dragons, a tome of the wyrm gradually increases the potency of its bearer's spells.
A tome of the wyrm describes dozens of battles between spellcasters and dragons (DC 10 Knowledge [arcana]). Wyrm wizards created the tomes to help them conduct research by overcoming the magical defenses of dragons, growing stronger over time (DC 20 Knowledge [arcana]).
A tome of the wyrm is a leather-covered grimoire with binding hinges and a back plate made of dark iron. An embossed, glowing eye with a slitted pupil adorns the cover. The eye remains heavily lidded unless a dragon attacks the tome's owner or the owner attempts a saving throw against a dragon's frightful presence. Then it opens wide until the battle is over.
Anyone can carry a tome of the wyrm, but its magic benefits only those who cast spells. A tome of the wyrm functions automatically, but only when carried in one hand. If it is left in a backpack or other container, it still records battles (as described below), but it doesn't improve its owner's caster level. A spellcaster carrying a tome of the wyrm in one band gains a +1 insight bonus to his caster level on any spell that targets an enemy dragon or includes an enemy dragon in its area. This benefit applies against all creatures affected by the spell, not just the dragon.
At the end of each of the caster's turns, determine whether he cast a spell that harmed an enemy dragon. (For the purpose of this item, this means any spell that dealt damage to the dragon, any spell against which the dragon failed a save, or any spell that overcame the dragon's spell resistance.) If so, the insight bonus of the tome of the wyrm increases by 1. If not, the insight bonus decreases by 1.
A tome of the wyrm's bonus can't drop below +1, nor can it rise above a number equal to the highest-level spell that its owner can cast. One hour after the last time the caster harms an enemy dragon with a spell, this effect fades, and the tome's bonus returns to normal. Each page of a tome of the wyrm describes one battle against a dragon - a brief narrative explaining who was present, how the fight unfolded, and how the dragon died (or how its attackers got away). After each new battle with a dragon, the tome magically adds a new page describing that battle. Once this 200-page book is full, any new entry overwrites the oldest entry.
Moderate divination; CL 10th; Craft Wondrous Item, detect dragonblood; 7,500 gp, 600 XP, 15 days; Weight: 5 lb.; Price: 15,000 gp.
Source: Dragon Magic