Does what it says on the tin, it measures the velocity of the BB that comes out of your gun. Very compact and solid, easy to bring around with you to your games. Its also got an folding display unit which can be removed. The display unit can be mounted on the BB gun tactic rail.What also makes this thing of a beauty is that it features wireless communications for both units.
Wonderful piece of technology the display unit shows rate of fire, initial velocity, BB information and memory of last 25 shots. The display unit needs 2 AAA batteries to run and the chrono unit needs 2 AA batteries, they dont come included.