In a spreadsheet program like iWork's Numbers for iPad, a checkbox can indicate, for example, that an item is in stock or out of stock (yes/no or true/false). However, you can also use it to represent numeric data.

Computers and programs often need to represent yes/no or true/false values (they're called Boolean values after the great mathematician George Boole). Boolean values consist of zeroes and ones; zero means false (or no) and one means true (or yes). In practice, it is often the case that zero means false and any other value means true. That's one way you can use checkboxes to track inventory. If you have the number of in-stock items in a cell, you can use a checkbox to indicate that there are none in stock (an unchecked checkbox) or that there are any in stock (a checked checkbox). Numbers will handle the conversion for you.

Here's how that can work:

1. Double-tap a cell to start editing it, and tap the Checkbox button as soon as the keyboard opens.

You'll see a checkbox in the selected cell; in the formula bar above the keyboard, you'll see the word false in a green outline. The green outline distinguishes it from text that you type in. It has the value false because before you've typed anything in, its numeric value is zero.

2. Type in a nonzero value.

This can represent the number of items in stock.

3. Tap the Checkbox button again.

You'll see that the value you typed is changed to true, and the checkbox is selected in the table.

Because the formatting is separate from the data value, you can sometimes display the in-stock inventory count as a number and sometimes display as the checkbox. All customers probably care about is the checkbox, but the inventory manager cares about the number.

With a cell selected and the Checkbox formatting button selected, you'll see the true/false value above the keyboard and the checkbox itself in the table cell. Tap the checkbox in the table cell: The true/false value is reversed, as is the checkbox itself.

Likewise, if you tap the word true or false in the display above the keyboard, the checkbox will flip its value, and true/false will reverse.

When you tap one of the formatting buttons, it turns blue and formats the number in the selected cell (or cells). You can tap another formatting button to switch to another format (from stars to a percentage, for example). Tapping a highlighted formatting button turns it off without selecting another: Your numbers are displayed the way you type them in.