Jennifer "JJ" Jareau:  Four numbers . What is that ? 3 , something , something , _ 6 _
Penelope Garcia: That 's a unit number , 4 digits ending with a 6 . 999 possible combinations
Jennifer "JJ" Jareau: Oh , but a unit number would be registered , right ?
Penelope Garcia: Already on it , kitten
Jennifer "JJ" Jareau: Of course you are
Penelope Garcia: That 's how I roll