Syncing Multipclips 1/100th of a Frame at a Time.

When you are positioning your playhead to the sync point of a clip (for example, for a multiclip sequence) that doesn't have synced timecode, or are just trying to get audio in sync or just need more precise control over where the playhead is in an audio clip in the Viewer, hold down Shift.

This will let you scrub and position the playhead in 1/100th of a frame increments. When you mark the In point you'll see FCP move things to the nearest frame to the point you positioned your playhead. It can help when you need precise sync and In point control. But this only works in Audio, not Video.