Formula Basics
On the surface, a formula cell looks just like any other. It displays the results of its calculation and looks for all the world like all the other cells whose values you typed directly into the table. Under the hood, though, the actual value of the cell is an equation—the formula—that tells Numbers how to generate that cell’s value. To see the formula, select the cell, and Numbers displays its formula in the Formula Bar, as shown in Figure 20-1.

Figure 20-1. This table shows students’ scores for assignments in the Basic Heroics class at the Up & Away sidekick academy. The selected cell in the last column shows the average score for the first student. Although its displayed value looks mild-mannered enough—just a simple percentage—the Formula Bar reveals its secret identity as a formula. Here, the formula calculates the average grade from the four cells in the row.
Don’t worry just yet about the structure and vocabulary of the formula in Figure 20-1; you’ll learn about the construction and building materials of formulas later in this chapter. For the moment, it’s important to understand only a few basics about the way formulas work:
A formula lives in a single cell. Even when a formula uses the values of other cells in its equation—to add up a column of numbers, for example—the formula always sits in the cell where the result is displayed.
Formulas always stay up to date. ...