Scuba & Nitrox Glossary: A
Nitrox and breathing-gas terminology is prioritized first. General scuba terms follow below. Definitions are educational summaries and do not replace formal training, manufacturer instructions, or an operational dive plan.
Nitrox & Gas Terms — A
- Actual Oxygen Percentage
- The oxygen fraction measured with an analyzer, not merely the requested or labeled blend.
- Air Equivalent Depth (AED)
- An older term often used interchangeably with equivalent air depth; EAD is more common.
- Analyzer
- An instrument used to measure oxygen concentration in a breathing-gas sample.
- Analyzer Calibration
- Setting or verifying an analyzer against a known gas before analyzing a cylinder.
- ATA
- Atmospheres absolute; pressure measured relative to a vacuum. At sea level the surface is approximately 1 ATA.
- Automatic Nitrox Mixing
- A continuous or controlled blending system that creates a target oxygen percentage during filling.
- Air Dilution
- Lowering oxygen percentage by adding suitable breathing air to a richer mixture.
- Analyzer Drift
- A gradual change in analyzer reading that requires recalibration and investigation.
- Analyzer Flow Restrictor
- A device that steadies sample flow across an oxygen sensor.
- ATA Calculation
- Using absolute atmospheres when calculating gas partial pressure at depth.
- Automatic Gas Switch
- A computer feature that changes active gas after diver confirmation or configured criteria.
General Scuba Terms — A
- Absolute Pressure
- Total pressure including atmospheric pressure at the surface.
- Alternate Air Source
- A backup second stage or other breathing-gas source intended for gas-sharing.
- Ambient Pressure
- Pressure surrounding a diver at a given depth.
- Anchor Line
- A line connected to an anchor, often used as a descent or ascent reference.
- Ascent Rate
- The speed at which a diver rises; it must remain within the limits of the plan, computer, and training.
- Air Consumption
- The rate at which a diver uses breathing gas.
- Air Integration
- A dive-computer feature that receives cylinder-pressure data and may estimate remaining gas time.
- A-Flag
- The international signal flag indicating a vessel has divers down and restricted maneuverability.
- Absolute Ambient Pressure
- Total surrounding pressure including atmospheric pressure, used in diving calculations.
- Accidental Separation
- Unplanned loss of contact between buddies or team members.
- Acclimatization
- Physiological adjustment to environmental conditions such as heat or altitude.
- Fixed Anchor Line
- A line associated with an anchor and often used for controlled descents or ascents.