1.2 Second functions
Notice that almost every key has more than one purpose or function. The main function is written directly on the key; but notice that written above the key, there is often another function. This is the second function for that key and is activated by first pressing and releasing the second-function key near the top left-hand corner of the keyboard. For example on the TI-84, OFF is the second function for the ON key: you press 2nd [OFF] to turn the calculator off.
On some calculators, some keys also have third functions, written above them. For example you may be able to type letters of the alphabet by first pressing an key.
This module uses the notation, similar to that used in the TI Guidebook, where the main function keys, like ON, are written in bold, whereas second function keys, like OFF, are written inside square brackets as in 2nd[OFF]. The number keys and alphabetic symbols are in bold type: for example, 8.