I want to get excel to turn to manual calculation for any workbook used.
I thought I could use an add-in to create an automatic procedure with the
workbook open event, in order to make it generic:

Sub Workbook_Open()
If Application.Calculation = xlCalculationAutomatic Then
Application.Calculation = xlCalculationManual
End Sub

However, this seems to work only on individual workbooks since the add-in
doesn't perform any action when I open a random workbook.

Any ideas?