A dive computer is an optional but popular device that displays at a minimum your current depth, maximum depth, bottom time, and remaining no-decompression time. You'll learn more about no-decompression times and dive computers later in this course.

Computers replace the need for a depth gauge and timing device. Some high-end computers also display your cylinder's remaining air pressure and replace the need to carry a separate submersible pressure gauge.

Other common features include a dive log, thermometer, and ascent rate indicator. If you plan on using a computer during this course, be sure to read its operating instructions and familiarize yourself with its displays and functions.