The Application.Calculation property is Application-wide. This means all
workbooks are affected when it is changed. Moreover, the state of
Application.Calculation is stored with a workbook when it is saved, so next
time you open that workbook, Application.Calculation changes to the state it
was in when that workbook was last saved. Confusing and sometimes
problematic.

- Jon
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Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
Peltier Technical Services, Inc. - http://PeltierTech.com
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"JLGWhiz" wrote in message
...
my first thought is that it would only affect the workbook that is active
at
the time the code is executed.

"snoopydoopy" wrote:

Using C# and Office Interop, I am opening 2 different copies of a
workbook (I manually copy workbook1.xls to workbook2.xls).Both
workbook1 and workbook2 have exactly same copies of the macros. From
the interop, I am calling macros in workbook1 and workbook2. I am
able to do this successfully but I am worried about 1 thing. At
different points in the macro, I call application.calculate and then
reset it back to manual. My worry is that the calculation settings in
one workbook would affect the processing of the other workbook.
Anybody can throw light on this?