The Modulus Ghost Ops ChronoBarrel accessory counts darts as battlers fire darts from their Nerf Modulus Ghost Ops Evader blaster (sold separately). Attach it the front of the blaster, then select to program the barrel to see how many darts have already been fired or the number of darts remaining in the blaster. The ChronoBarrel accessory also measures the velocity of the darts being fired in either feet or meters per second. Built-in memory also remembers the last number of darts set in the count-down mode. It comes with 6 darts. The barrel and is also compatible with other Nerf Modulus blasters. Nerf Modulus Ghost Ops battlers can upgrade their blaster with the Ghost Ops ChronoBarrel accessory to keep track of their darts and dart velocity! (Blasters each sold separately.) Counts darts as battlers fire their blaster Measures dart velocity in feet or meters Part of the Modulus Ghost Ops series Customize Modulus blasters Nerf and all related properties are trademarks of Hasbro. Includes: barrel, 6 darts, and instructions. Ages 8 and up. Caution: Do not aim at eyes or face. To Avoid Injury: Do not modify darts. Warning: Choking Hazard - Small parts may be generated. Not for children under 3 years. Requires 2 AA alkaline batteries (not included)