Rockwell Automation FactoryTalk Historian SE DataLink 4.2 User Guide - Manual (Page 71)

Chapter 6
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Spreadsheets
When you add a function to a spreadsheet, FactoryTalk Historian DataLink
retrieves the requested data from the FactoryTalk Historian server into an
array. The size of the array can vary depending on the function, how many
matching archive values are available in FactoryTalk Historian, the number
of values requested, or the number of input references.
The following topics provide an overview of how FactoryTalk Historian
DataLink functions work within a spreadsheet, and how to manage and
maintain your spreadsheet over time.
Calculation Frequency
You can choose an automatic update interval to keep function data current
in your spreadsheets, or use function-triggered and manual recalculation
methods used in previous versions of FactoryTalk Historian DataLink.
For detailed information on how Excel manages calculation, see the Excel
Recalculation (http://msdn.microsoft.com/en-us/library/bb687891.aspx)
topic in the MSDN library.
Automatic Update
Automatic Update forces Excel to recalculate functions and trends on open
worksheets at a specified interval. To activate Automatic Update:
Click the Update toggle button on the PI ribbon (2007), or choose
Update from the FactoryTalk Historian menu (2003).