When you change any cell in a work sheet. Excel automatically recalculates the whole worksheet to keep it up to date. But if you have a huge worksheet or terribly slow computer, this behav¬iour will hog more time to calculate than to enter data. One way to get over it is to change the default behaviour to manual worksheet calculation:

1.Click Office button and choose Excel Options

2.In the left side column, click on Formulas and scroll to Calculation Options in the right side column.

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1.Select the Manual radio button which ensures the workbook calculation is done manually.

2.Click OK to complete. For manual cal¬culation, hit [ F9] for the final changes to reflect in the workbook.