| AA |
Assisted Ascent |
|
AAS |
Alternate Air Source, second demand valve or regulator, sometimes referred to an octopus. |
| Abaft |
Behind, toward a vessel's stern. |
| ABC |
Airway, Breathing, Circulation |
| Abeam |
Off to the side, amidships, at right angles to vessel |
| Absolute Pressure |
Absolute pressure is a measure of the pressure exerted on an object from all sources; includes water pressure and atmospheric pressure. |
| ABLJ |
Adjustable Buoyancy Life Jacket. An older style of buoyancy device still used by some divers. |
| A Clamp |
A type of fitting for connecting the regulator 1st stage to the cylinder pillar valve. |
| ACI |
Assistant Club Instructor. A BSAC instructor qualification. |
| ACR |
Air Consumption Rate, same as SAC, Surface Air Consumption. |
| AD |
Advanced Diver. A BSAC diver qualification. |
| Adrift |
Unattached to shore or bottom, floating out of control |
| A Flag |
The international flag 'A' .  Used to denote diving activities |
| AGE |
Abbreviation for Arterial Gas Embolism. See CAGE. |
| Aground |
Touching or stuck on the bottom. |
| AI |
Advanced Instructor. A BSAC instructor qualification |
| Air embolism |
Bubble of air in the blood stream that causes a blockage. |
| Alee |
Away from the direction of the wind. Opposite of windward |
| algorithm |
A mathematical formula |
| Almanac |
A calender giving time of such events as sunrise and sunset, changes of moon and tides, change in position of celestial bodies, or other special information. Particularly necessary for celestial navigation. |
| Aloft |
Above the deck of a boat. |
| Alternate Air Source |
Any device a diver can use in place of the primary regulator. |
| Atmospheric Pressure |
The amount of pressure the air around us exerts on our bodies at sea level, about 14.7 pounds of pressure per square inc |
| Alveoli |
Small air cells in the lungs. |
| Ambient pressure |
The surrounding pressure; on land this comes from the weight of the atmosphere; at depth it is the sum of both the weight of the atmosphere and the weight of the water. |
| Amidships |
In or near the middle of the boat. |
| Anchorage |
A place that is suitable for anchoring considering the wind, current, seas and bottom. |
| Anoxia |
The total lack of Oxygen to the tissues. Also see Hypoxia |
| Anticyclone |
High Pressure area, usually associated with settled weather, in the Northern hemisphere an anti-cyclone circulates clockwise. |
| AOW |
Advanced Open Water. A PADI diver qualification |
| AP |
Absolute Pressure |
| Apnea |
Cessation of breathing for short intervals of time. If left untreated it will proceed to respiratory arrest. |
| Argon |
An inert gas which is very narcotic in the normal diving range, twice that of Nitrogen. It is a good insulator however and sometimes used in diving suits. |
| Ascent Check Depth |
A point reached during the ascent where dive time is checked against the plan. This is usually at the first decompression stop or 6m for no-stop dives. |
| Ascent Rate |
The speed in which a diver ascends. BSAC recommend 15m/min up to 6m and then 6m/min for the final 6m. |
| Astern |
At any point behind the boat, backward. |
| ATA |
Atmospheres Absolute |
| Atmospheric Pressure |
The local atmospheric pressure produced at a particular altitude by current weather conditions. |
| Auto Air/Air II |
A form of alternate air source build into BuddyT stab jackets. |
| AV |
Artificial Ventilation |
| Azimuth |
Vertical arc of sky from zenith (point of heavens directly above observer) to horizon (line at which earth and sky or sea and sky appear to meet); angular distance of this from a meridian. |
