The REC (Record) button activates capture of a/v data to file(s) on assigned storage volumes on or off. (The specific sources that are recorded are configured in Startup when creating the session; see Section 10.1, and also 10.3.1).
Note that simply pushing REC again does not disable recording. To prevent accidental interruptions in capture of important events, you must hold down SHIFT before pressing REC when you wish to stop recording.
Tip: As a helpful reminder, a special ‘record event’ row is added to the CLIP LIST whenever newly you enable 3Play recording.