The middle two buttons on the top row stop and start the song playing. They are useful for aligning songs which are slightly out of sync. These buttons are useful to move around within the song while staying on beat. The anchor button will set the turntable to be the lead source. This means that if it is playing, other songs can sync to it.
Turntables can resample their songs to match any tempo.
To cause one turntable to resample its song to match another song's tempo, drag and drop the desired tempo from one turntable's bpm label to the other turntable's resampling area. This allows one to sync an 80 bpm song to a 160 bpm one, without extensive resampling. Buttons Without Modifier - Starts the song playing. If the song is already playing, synchronize this song with the lead song. Both songs must have beat information in the song database for this to work.