Number formatting affects perceived precision in Excel for Mac (181918)

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When you format numbers by clicking Cells on the Format menu, you alter the way Excel for Mac displays the numbers; however, when you calculate numbers, Excel for Mac performs the calculations by using the stored values. When you calculate formatted values, you may receive unexpected results because the displayed numbers may be slightly different from the stored values.

For example, if two cells each contain the value 10.005, and the cells are formatted to display values as currency, the value $10.01 is displayed in each cell. If you add the two cells together, the result is $20.01 because Excel for Mac adds the stored values (10.005 + 10.005), not the displayed values ($10.01 + $10.01).

If you want the calculations to be based on the displayed values, you can change the precision of calculations so that they use the displayed values instead of the stored values. To do this, use the Precision As Displayed feature or make sure that the values are rounded to the same precision as the number formatting.

Round Values to the Same Precision as Number Formatting

You can use the ROUND worksheet function to round values to a specific precision.

Example:

For this example, type the following in a new worksheet:

   $A$1: $10.005
   $A$2: $10.005
   $A$3: =SUM(A1:A2)
				

The resulting values in the cells appear to be:

$A$1: $10.01 
$A$2: $10.01 
$A$3: $20.01

This gives the appearance of an error in calculation, as stated earlier. To round the precision to reflect the apparent resulting value in A3, replace the entries with the following:

    $A$1: =ROUND(10.005,2) 
    $A$2: =ROUND(10.005,2) 
    $A$3: =SUM(A1:A2)
				

If you now use the currency format, the following values are displayed:

$A$1: $10.01 
$A$2: $10.01 
$A$3: $20.02 

When you do this, the worksheet function takes the result of the expression in the first argument and rounds it to the hundredth's place (two digits to the right of the decimal).

Round All Values in a Worksheet by Using Precision As Displayed

If you want the calculations to be based on the displayed values, change the precision of calculations so that they use the displayed values instead of the stored values. To do this, follow these steps:

1. Use the appropriate method for your version of Excel for Mac.

   Microsoft Excel X for Mac and later versions of Excel for Mac

   On the Excel menu, click Preferences, and then click Calculation in the left pane.

   Microsoft Excel 2001 for Mac

   On the Edit menu, click Preferences, and then click the Calculation tab.

   Microsoft Excel 98 Macintosh Edition

   On the Tools menu, click Preferences, and then click the Calculation tab.
2. Under Workbook Options, click to select the Precision as displayed check box.

CAUTION: When you change the precision of the calculations in a workbook by using the displayed (formatted) values, Excel for Mac permanently changes any constant values on the worksheets in the workbook. If you then calculate values with full precision, Excel for Mac cannot restore the original underlying values.