The Residual Nitrogen Time or RNT is a way to convert the saturated nitrogen in the body in time to be easier to use with tables.
The NDL or No Decompression Limit is a period of time that a diver can stay according to the depth before decompression is required. The NDL is used in recreational diving to calculate the maximum time a diver can stay and is used when planning dive. Dive computers will calculate this limit at set interval normally in just a few seconds to accommodate changes in depths through the dive.
The work of breathing or WOB is in simple terms, the effort required by the lungs to breathe. But to be more accurate it refers to the energy expended to inhale and exhale a breathing gas. The WOB is usually expressed as work per unit volume.
Divers Alert Network or DAN is a non-profit agency that collects and analyze information for divers safety. It has branches that sell different diving oriented services and products such as insurance or oxygen providing kits or First Aid and CPR courses.
The SI or surface interval is the amount of time between 2 dives which is used to calculate the limits in consecutive dives.
The gauge pressure is the pressure shown by a gauge which was calibrated and zeroed using ambient surface pressure at sea level as a reference.
fsw or feet of seawater is a measurement unit of the imperial system and represent the pressure in 1 foot of seawater or about 15 psi. 33 feet is also roughly 1 atmosphere.
Its was in 1971 in Canada that the DCIEM or Defence and Civil Institute of Environmental Medicine was founded in a joint participation of military and civilian personnel. This lead to the development of dive tables that were more conservative than the US Navy tables.
Open circuit is the breathing system most commonly used for scuba diving. It is called open circuit because all the gas exhaled by the diver is expelled in the environment. A basic OC breathing apparatus is composed of a cylinder, a regulator first and second stage and a pressure gauge. The other systems are called CCR for closed circuit rebreather or SCR for semi-closed rebreather because they reuse in a loop all or part of the diver exhaled gas.
MSW or Metre Sea Water is the unit used in metric to measure the pressure divers are exposed to. For every meter of sea water the pressure is theoretically 0.1bar and is equal to 3.26336 fsw.