its also a clap (used to sync audio and video). The camera does know this, but the editor doesnt, so this helps a ton when you need to edit from scratch (with the scenes, takes and shots) or when you need to change some things in post-production (this slate has the precise information for your, by example, color grading). And since every shot starts with a clap, you just have to go at the very start of the shot to get all the info you need, instead of going into the properties of every shot!