radio station nowplaying

Hi All!

I am working on a website for a radio station and I am trying to get a handle on the logic behind the current program block. I have the station and the now playing modules installed on my development system. I understand that the now playing module can be setup to take the songs that are playing from a shoutcast server in addition to the schedules that are setup. How does the block determine whether to use the songs from the shoutcast stream or the schedule?