The MT 48 by default will follow its internal clock when used by itself as a USB C interface.
But when incorporating with other audio gear, it is very important that one device is made Master, and the other device (or devices) are set to follow the master - known as slave.
These settings are found in Menu > Settings > General > Clock on the MT48.
Internal - The MT 48 is using its own clock. Default option with one MT 48 connected to a computer over USB C.
RAVENNA/AES67 - The MT48 is following a connected AES67 device - for example, a Hapi mk II or III, or Anubis.
Optical - The MT 48 is slaving or following over it's ADAT IN port connection
When the MT 48 is set to follow another device - that other device must be set to be the Master clock in its settings. And vice versa - if the MT 48 is set to be the leader (traditionally the case if being USB connected) - the secondary device must be set to follow accordingly through its clock settings.
If the Sync Source has a green box next to its highlighted selection, that indicates a successful synchronization and you are good to go.
A yellow box indicates clocking in progress ; and a red box indicates improper sync and should be further verified and corrected.
Sampling rates must match when synchronizing two pieces of gear.
PTP Status indicates whether the device is Master, or Slave. This is also displayed on the top banner of the MT48, indicated by a green M or S.
Lastly, over USB, the ASIO Clock can be set to Auto or Off. This will only become relevant in AES67 network scenarios when the MT 48 must generate it's own PTP clock.