The Function-keys checkbox is a checkbox in the Keyboard Control Panel that lets the user choose whether the function keys F1-F12 are primary or secondary. Function keys primary means the function keys default to their F1-F12 functions when the the Fn key is not depressed. Function keys secondary means the function keys default to their control-button behavior when the the Fn key is not depressed. In either case, pressing the Fn key reverses the functions of the function keys from the default functions set by the checkbox. The two sets of functions of the function keys are shown in Table 3-5 and Figure 3-5 .