This is an analyzer sequence parameter which identifies the acquisition by number.
Acquisitions are numbered sequentially (1 through n), and executed sequentially (one acquisition must end before the next acquisition begins).
Acquisitions are numbered automatically as they are added to the table; any changes you make to the numbers in this field will be overwritten by the automatic sequence.
The process for adding acquisitions to the table is described in Editing the Analyzer Sequence Parameter Table.