276 NAUI Master Scuba Diver GLOSSARY Mass: The quotient obtained by dividing the weight of a body by the acceleration due to gravity. Matter: The substance of which any physical object is composed. Maximum depth indicator: An indicator of a mechanical depth gauge that is pushed along by the needle of the gauge and which remains at the maximum reading attained by the instrument. MSW: Meters Sea Water. Multi-level diving: A dive with time spent at more than one depth, especially a progression from deeper depths to shallower depths. N Neap tides: Those tides with the minimum range between high water and low water. Nektonic: Free-swimming forms of life, including fish, which rely on speed and streamlining for their survival. No-Decompression Limit: The maximum time that can be spent at a given depth resulting in a dive with no required decompression stops. O Octopus: An extra second stage attached to a scuba regulator. Offgassing: Gas dissolved in a liquid coming out of solution. Open circuit demand scuba: A system in which compressed air is inhaled upon demand from a self-contained unit and exhausted into the environment. Orifice: An opening or aperture of a tube, pipe, etc. P Panic: The emotional and volatile human reaction which occurs in the presence of a real or imagined danger; characterized by a total loss of logic and mental control. Parenteral toxins: Toxins delivered by means of a venom apparatus. Partial pressure: The pressure exerted by each individual gas within a mixture of gases. Pascal’s Principle: Pressure in a fluid is transmitted uniformly in all directions. Peer pressure: The pressure placed by peers on fellow divers. Phytoplankton: Drifting algae that use sunlight to produce carbohydrates. They represent the basic food source for all life in the oceans. Pilotage: Navigation confirmed with visual check points. Pilot-valve regulator: A regulator second stage main valve that is opened and closed using air pressure rather than mechanical leverage. Planktonic: Drifting and floating forms of life carried passively by currents. Plunging breakers: Surf that peaks quickly and breaks suddenly when large swells approach a shore with a moderately steep slope. Pressure gradient: The difference between the tension of a gas in a liquid and the partial pressure of the gas outside the liquid. Propulsion: The act of driving forward. R Range: A line of position indicated by a set of in-line objects. Rebreather: A closed-circuit diving system which
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