Apple Logic Pro 9 - Manual (Page 948)

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Choose a number from the Alternative pop-up menu in the Signature List.
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Choose a number from the Alternative pop-up menu in the Signature track.
For full details about inserting signatures, see Creating Time Signatures and Creating Key
Signatures .
To switch between signature alternatives
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Choose the appropriate number from the Alternative pop-up menu in the Signature track
or Signature List.
All MIDI regions are affected, resulting in the appropriate changes to your score.
948 Chapter 31 Working with Notation