What is the default FO2 setting for most dive computers?

The default FO2, or fraction of oxygen, setting for most dive computers is 21 percent, which corresponds to the percentage of oxygen found in regular air. This is significant because, when not using a special gas mix like Nitrox, divers typically breathe air composed of approximately 21 percent oxygen.

This setting is crucial for calculations related to decompression and allows divers to accurately track their nitrogen absorption and saturation levels during dives. When divers switch to using Nitrox, they would adjust this setting according to the specific gas being used, but the baseline for dive computers is 21 percent to ensure that they provide accurate and safe information for air diving scenarios.

Understanding this default value helps divers recognize how adjustments to the FO2 value impact their dive planning and safety, especially as they transition to using enriched air Nitrox mixes.