NASDS: National Association of Scuba Diving Schools
NAUI: National Association of Underwater Instructors
NDC: National Diving Council
NDL: No Decompression Limit
NDO: National Diving Officer
NDS: No Decompression Stop
NDSTC: Naval Dive and Salvage Training Centre
NEC: National Exhibition Centre
NED: Network of Egghead Divers
NEDU: Naval Experimental Diving Unit
NERC: National Environment Research Council
NHC: National Hyperbaric Centre
NI: National Instructor
NMRI: Naval Medical Research Unit
NOAA: National Oceanic and Atmospheric Administration
NSB: Natal Shark Board
NSS: National Speleological Society
NSS-CDS: National Speleological Society-Cave Diving Section
OD: Ocean Diver
OMS: Ocean Management Systems
OOA: Out of Air
OS: O.S. Systems, Inc.
OSHA: Occupational Safety and Health Administration
OSTC: Open Source Tauchcomputer
OTT: Oxygen Tolerance Test
OTU: Oxygen Toxicity Unit
OW: Open Water
OWD: Open Water Diver
OWI: Open Water Instructor
OWIC: Open Water Instructor Course
OWSI: Open Water Scuba Instructor
P: Pressure
PADI: Professional Association of Diving Instructors
PADUA: Pennsylvania Analysis of Decompression for Undersea and Aerospace
PDC: Personal Dive Computer
PDIC: Professional Diving Instructors Corporation
PFO: patent foramen ovale
PG: Pressure Group
pp: partial pressure
PPB: Peak Performance Buoyancy