Seeker

This property provides an enhancement bonus to confirm critical hits and critical hit damage. A +10 Seeker item will add +10 to your confirm critical roll and +10 (times your critical multiplier)to your critical damage.

The Seeker effect from items and weapons does not stack, only the single highest bonus applies. So, you only need it on one of your weapons or on an item (such as Bloodstone or Shimmering Arrowhead).

The Seeker bonus will be used for all attacks (single weapon melee, dual weapon melee, and ranged), so it can be useful to hold a Seeker +10 weapon in your off-hand when using a thrown weapon.