Sync Mode pop-up menu: Defines how Logic Pro syncs with the other device.
Internal: Selects the internal timer of Logic Pro, with Logic Pro transmitting MIDI clock. External devices can be synchronized via MIDI clock or MTC.
MTC: Selects MIDI Time Code mode, with Logic Pro following incoming MTC. MIDI timecode can either arrive at a MIDI In port, or be generated by a MIDI interface that translates it from incoming SMPTE timecode—the Unitor8, for example.
Manual: Selects Tempo Interpreter mode, with Logic Pro receiving MIDI clock impulses that are recognized as valid beats by the Tempo Interpreter. The parameters that control how Logic Pro responds to Tap Tempo commands can be found in the Apple Books | PDF