Excel's Formula - sisman

Chapter 4: Introducing Worksheet Functions 117
Other function categories
In addition to the function categories described previously, Excel includes four other categories
that may not appear in the Paste Function dialog box: Commands, Customizing, Macro Control,
and DDE/External. These categories appear to be holdovers from older versions of Excel. If you
create a custom function, you can assign it to one of these categories. In addition, you may see
other function categories created by macros.
See Chapter 23 for information about assigning your custom functions to a function
category.
Volatile functions
Some Excel functions belong to a special class of functions called volatile. Excel recalculates a
volatile function whenever it recalculates the workbook — even if the formula that contains the
function is not involved in the recalculation.
The RAND function represents an example of a volatile function because it generates a new random
number every time Excel calculates the worksheet. Other volatile functions include
● CELL
● INDIRECT
● INFO
● NOW
● OFFSET
● TODAY
As a side effect of using these volatile functions, Excel always prompts you to save the workbook
when you close it — even if you made no changes to it. For example, if you open a workbook
that contains any of these volatile functions, scroll around a bit (but don’t change
anything), and then close the file. Excel asks whether you want to save the workbook.
You can circumvent this behavior by using the Manual Recalculation mode, with the Recalculate
Before Save option turned off. Change the recalculation mode in the Calculate section of the
Formulas tab in the Excel Options dialog box (choose File➜Options).