WORKSHEET FUNCTIONS are special tools that perform complex calculations quickly and easily. They work like the special keys on sophisticated calculators that compute square roots, logarithms, and statistical evaluations—except Microsoft Excel has hundreds of these special functions. Some functions, such as SIN and FACT, are the equivalent of lengthy mathematical formulas you would otherwise have to create by hand. Other functions, such as IF and VLOOKUP, can’t be otherwise duplicated by formulas. When none of the built-in functions is quite what you need, you can create custom functions, as explained in Chapter 29.