You must stay out of the water for at least 24 hours before using a computer for the first time, and that computer must be used on all repetitive dives. This ensures that the nitrogen levels stored in the computer are accurate to your actual levels.

If your computer fails during a dive, immediately make a safe ascent to the surface. Remain out of the water for 24 hours, and have the computer inspected and repaired before using it again.

Forgetting to turn on or activate your computer before descending can result in inaccurate pressure readings. If you discover that you forgot to activate your computer, immediately make a safe ascent to the surface, activate your computer, and resume the dive. Many computers contain water sensors that automatically activate the computer when they become wet. If the computer you use has this feature, it's still a good idea to manually activate the computer before beginning a dive. This helps to ensure the computer operates correctly before beginning the dive.