RIGOL DS6000 Series - Manual (Page 248)

RIGOL 13 System Function Setting
DS6000 User’s Guide 13-16
Reference Clock
This oscilloscope can output the internal 10 MHz sample clock from the [10MHz
In/Out] connector at the rear panel and accept an external 10 MHz clock to
synchronize multiple oscilloscopes.
Press UTIL  RefClock to select the desired clock type.
 ClockOutput: configure the [10MHz In/Out] connector as an output and
output the internal 10 MHz clock.
 ClockInput: configure the [10MHz In/Out] connector as an input and the
oscilloscope will accept an external 10 MHz clock input from this connector.
10MHz In/Out