Frank Rice has written a "show how" about creating functions that are not included in the box.
"Excel allows you to create custom functions, called "User Defined Functions" (UDF's) that can be used the same way you would use SUM(), VLOOKUP, or other built-in Excel functions.
The Excel user who wishes to use advanced mathematics or perform text manipulation is often seriously disappointed by Excel's limited library of formulas and functions. A UDF is simply a function that you create yourself with VBA.
The following is a sample that is a good candidate for a UDF:
CtoF = Centigrade * 9 / 5 + 32
In the Worksheet you would enter something like: =CtoF(A1)