Editing : Edit Modes and Tools : Grid Mode : Absolute and Relative Grid

Absolute and Relative Grid
Grid mode can be applied in Absolute or Relative mode:
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In Absolute Grid mode, moving any clip snaps the clip start to Grid boundaries. If a clip’s start point falls between beats, and the Grid is set to 1/4 notes, dragging the clip will snap its start time to the nearest 1/4 note (the current absolute Grid value).
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In Relative Grid mode, clips can be moved by Grid (or Nudge) units. If a clip’s start point falls between beats and the Grid is set to a 1/4 note (assuming the 1/4 note gets the beat), dragging the clip will be constrained to 1/4 notes, preserving the clip’s relative position to the nearest beat. For more information on Relative Grid mode, see Sliding Clips in Grid Mode.
To select Absolute or Relative Grid mode:
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To temporarily suspend Grid mode and switch to Slip mode while dragging a clip, hold the Control key (Windows) or Command key (Mac) after clicking the mouse.