Controlling Calculation
Excel has a range of options allowing you to control the way it calculates.
You can change these options using the Tools >Options>Calculation
tab.
Calculation Settings Keep Changing
Because a number of Excel's calculation settings work at the application
level (they are the same for all open workbooks), and are set by the
first workbook opened, they may appear to change randomly depending
on the sequence in which workbooks are opened. FastExcel Version 2
allows you to solve many of these problems.
Automatic Calculation.
Automatic calculation mode means that Excel will automatically recalculate
all open workbooks at each and every change, and whenever you open
a workbook.
Usually when you open a workbook in Automatic mode and Excel recalculates
you will not see the recalculation because nothing will have changed
since the workbook was saved.
An exception is when you open a workbook in Excel 2000 that was saved
using Excel 97, or you open using Excel2002/2003 a workbook saved
in Excel2000: because the Excel calculation engines are different
a Full calculation is done.
Manual Calculation.
Press F9 if the status
bar shows “Calculate” 
Manual calculation mode means that Excel will
only recalculate all open workbooks when you request it by pressing
F9 or CtrlAltF9, or when you Save a workbook.
For workbooks taking more than a fraction of a second to recalculate
it is usually better to set Calculation to Manual.
Excel tells you when the workbook needs recalculation by showing
Calculate in the status bar. If this message won’t disappear
see Status bar shows Calculate
. 
Automatic except Tables.
Excel’s Data Tables feature is designed to do multiple calculations
of the workbook, each driven by different values in the table. So
using Automatic except Tables will stop Excel from automatically triggering
the multiple calculations at each calculation, but will still calculate
all dependent formulae except tables.
Application level settings.
The following calculation settings are held at the Application level
rather than for each workbook, so they apply to all open workbooks.
 Calculation Mode (Automatic, Automatic except Tables, Manual,
Calculate before Save).
 Iteration settings (Iteration On/Off, Max Iterations, Max Change).
Rather confusingly these application level settings are saved in
each workbook, but only the settings in the first workbook opened
are actioned: the settings in subsequent workbooks are ignored.
Workbook level settings.
The following calculation settings are held at workbook level, so
each open workbook can have different settings.
 Update remote references.
 Precision as displayed.
 1904 date system.
 Save external link values.
 Accept labels in formulae.
All these workbook level calculation settings are saved and restored
with the workbook, except Update remote references.
Controlling Excel’s Calculation Options.
FastExcel Version 2 significantly extends Excel’s calculation
options. See the FastExcel Version 2 User Guide for details.
The details below refer to Excel’s standard calculation options.
Calculation Mode operates
at Application rather than Workbook level. 
When Excel has no workbooks open, or when you
start Excel, it sets the initial calculation mode and settings
from the first nontemplate, nonaddin, nonPersonal.xls
workbook that you open
This means that the calculation mode setting in subsequently
opened workbooks will be ignored, although you can change the
mode yourself at any time using Tools>Options>Calculation.
As soon as you change the calculation mode, it applies to all
subsequently opened workbooks.
If you want to override the way Excel sets the initial calculation
mode you can set it yourself by creating a module in ThisWorkbook
(doubleclick ThisWorkbook in the Project Explorer window in
the VBE), and adding this code. This example sets calculation
to Manual.
Note that this will NOT prevent the workbook being recalculated
if it is opened in Automatic mode.
Private Sub Workbook_Open()
Application.Calculation = xlCalculationManual
End Sub
If calculation is set to Automatic when a workbook containing
this code is opened, Excel will start the recalculation process
before the Open event is executed. You can bypass this problem
by:
 Using FastExcel version 2's Initial Calculation setting.
 Have a single workbook (as long as its not called Personal.xls)
in your XLSTART directory which has been saved in Manual mode.
 Have an Addin installed which sets calculation to manual
in its WorkBook_Open or Auto_Open procedures (Excel 97 and
Excel 2000 only).
If you have a workbook that was saved in Automatic mode, but
you want to open it in Manual mode:
 Open Excel with a blank workbook.
 Switch to Manual (Tools>Options>Calculation).
 Open the workbook that was saved in Automatic.
If you have a workbook that was saved in Manual mode, but you
want to open it in Automatic Mode:
 Open Excel with a blank workbook.
 Switch to Manual (Tools>Options>Calculation).
 Then switch back to Automatic. The two steps are required
to lock in the mode change.
 Open the workbook that was saved in Manual.

Excluding Worksheets from Recalculation.
You can prevent worksheets from being calculated or recalculated
by using VBA to set the Worksheet.EnableCalculation property to False.
See Calculating from VBA.
Note that this setting is NOT saved with the workbook.
FastExcel Version 2 gives you much better control over which worksheets
are calculated using FastExcel MixMode settings.
Recalculate before Save
In Manual mode this checkbox controls whether Excel will recalculate
the workbook as part of the save process. The default is Yes.
Iteration
Usually it pays to
uncheck the Iteration box. 
If you have intentional circular references in
your workbook, these settings allow you to control the maximum
number of times the workbook will be recalculated (iterations)
and the convergence criteria (maximum change: when to stop).
The default should be to uncheck the iteration box so that
Excel does not try to solve accidental circular references. 
Update Remote References.
If TRUE Automatically update any remote references (DDE Links to
other programs) whenever Excel recalculates.
Precision as Displayed.
Checking this box will force Excel to calculate to the number of
decimal places that appear as a result of your formatting, and will
permanently change any numbers stored in cells.
You need to be sure you have thought through the full implications
of this before using it.
Precision as Displayed slows down calculation.
1904 Date System.
If TRUE changes the starting date from which all dates are calculated
from January 1 1900 to January 2 1904.
Save External Link Values.
If TRUE Excel saves values for links to external workbooks. I recommend
keeping this option as TRUE.
Accept Labels in Formulae.
This allows Excel to try and using “natural language” labels in formulae.
Because there are circumstances where this will give you unexpected
or ambiguous results, I recommend you do NOT use this feature.
