Editing Scuba set (section)

==Accessories==
===Buoyancy compensator===
In most scuba sets, a [[Buoyancy compensator (diving)|buoyancy compensator]] (BC) or buoyancy control device (BCD), such as a back-mounted wing or stabilizer jacket (also known as a "stab jacket"), is built into the harness. Although strictly speaking this is not a part of the breathing apparatus, it is usually connected to the diver's air supply, to provide easy inflation of the device.  This can usually also be done manually via a mouthpiece, in order to save air while on the surface, or in case of a malfunction of the pressurized inflation system. The BCD inflates with air from the low pressure inflator hose to increase the volume of the scuba equipment and cause the diver gain buoyancy. Another button opens a valve to deflate the BCD and decrease the volume of the equipment and causes the diver to lose buoyancy. Some BCDs allow for integrated weight, meaning that the BCD has special pockets for the weights that can be dumped easily in case of an emergency. The function of the BCD, while underwater, is to keep the diver neutrally buoyant, ''i.e.'', neither floating up nor sinking. The BCD is used to compensate for the compression of a wet suit, and to compensate for the decrease of the diver's mass as the gas from the cylinders is used up.<ref name="PADI BCD" />

===Ballast===
{{Main|Diving weighting system}}
Ballast is used to increase the average density of the scuba diver and equipment to compensate for the buoyancy of diving equipment, particularly the diving suit, allowing the diver to fully submerge with ease by obtaining neutral or slightly negative buoyancy.  Weighting systems originally consisted of solid lead blocks attached to a belt around the diver's waist, but some diving weighting systems are incorporated into the BCD or harness. These systems may use small nylon bags of lead shot or small weights which are distributed around the BCD, allowing a diver to gain a better overall weight distribution leading to a more horizontal [[Diver trim|trim]] in the water. Tank weights can be attached to the cylinder or threaded on the cambands holding the cylinder into the BCD.<ref name="Scubadoc" />

===Monitoring instruments===
{{See also|Submersible pressure gauge|Diving rebreather#Control of the breathing gas mix}}
The basic instrument for monitoring available gas is the submersible pressure gauge, which indicates the remaining pressure in a scuba cylinder, by directly measuring pressure at a high-pressure port of the regulator first stage. Recreational divers commonly mount the SPG in a rubber or plastic {{visible anchor|console}} along with other instruments like a compass, depth gauge and/or [[dive computer]]. An alternative to the SPG is a [[pressure transmitter]] fitted to a high pressure port that wirelessly transmits the cylinder pressure to the [[dive computer]] for display, a system known as [[air integration]].<!--get ref from Dive computer article-->

Many closed circuit rebreathers use advanced [[electronics]] to monitor and regulate the composition of the breathing gas.<ref name="PADI RB" />

===Labelling of contents===
{{see also|Gas blending for scuba diving#Identification of cylinder contents}}
The composition of the gas in the scuba cylinder is analysed before use and recorded on a label on the cylinder. This is usually done directly after filling, when handing the cylinder over to the intended user, and when assembling the scuba set for use. The filler is responsible for ensuring that the mixture is within tolerance of the customer's specification, and the user, or in some cases the instructor, is responsible for ensuring that the mixture is suitable for the planned dive. Each person who analyses the gas is responsible for ensuring that the analysis matches the label on the cylinder. The default value is air, which does not always require a specific label. If the gas is air and the cylinder is identified for air only by colour code or labeling it man not be obligatory to analyse the contents.<ref name="SANS 10019:2008" />

===Mouthpiece retaining straps===
<!-- target for redirect [[Regulator necklace]], [[Mouthpiece retaining strap]] -->
A [[mouthpiece retaining strap]] (MRS) is an item of safety equipment which is a mandatory design feature for rebreathers sold in the EU and UK, following European rebreather standard EN14143:2013. Mouthpiece retaining straps have been shown in navy experience over several years to be effective at protecting the airway in an unconscious rebreather diver as an alternative to a full-face mask. The arrangement is required to be adjustable or self adjusting, to hold the mouthpiece firmly and comfortably in the user's mouth, and to maintain a seal. The MRS also reduces stress on the jaw during the dive.<ref name="RTC MRS" />

Mouthpiece retaining straps have also been used with open circuit scuba, both on single hose and twin hose units. They were quite common as original manufacturer's equipment in the 1960s, when they were usually called neck straps,<ref name="Basic Scuba" /> but at some stage lost popularity. The technical diving community later developed a similar functioning accessory generally referred to as a {{visible anchor|reguator necklace}} or bungee necklace, an aftermarket or home made elastic loop, generally used to hold the secondary demand valve in a position under the chin where it can be accessed hands-free by tilting the head.<ref name="Jablonski 2006" /> It can also be used to hold a primary demand valve in the same way, which will keep it in close proximity to the face if accidentally dropped or dislodged, making it often possible to recover hands-free. This type of retainer does not necessarily keep the mouthpiece in place in the diver's mouth or maintain a seal if the diver loses consciousness, as the fit is not always adjustable. The bungee necklace can be pulled away from the neck with a moderate force, causing the rubber mouthpiece to pop out of the retaining loop.<ref name="Davis b" />

===Hose swivels===
Swivel fittings between the low pressure hose and the second stage inlet connection are available which allow either a fixed angle or a variable angle between hose and demand valve housing. These allow a wider range of comfortable hose routings, particularly useful for stage and side-mount cylinders, but add another potential point of failure at the swivel joint. Swivels are also occasionally used between first stage and hose to provide better hose routing, but these usually have a fixed angle. The two types are not interchangeable, and can be recognised by the thread and O-ring arrangement.<ref name="Mark" />

===Second stage isolation valve===
A manually operated shut-off valve may be fitted between the low-pressure hose and the second stage, which can be used to isolate the second stage in a free-flow, or at any time when it is necessary. When this is fitted, an over-pressure relief valve us necessary on the first stage. Low profile valves operated by sliding an axial sleeve are available for this purpose and are less likely to snag than a quarter-turn ball valve, and are faster to operate than a screw-down valve, such as is standard on diving helmets for bailout.<ref name="Zeagle" />

===Adaptor for full-face mask===
Adaptors for some second stages are available to connect them to some models of [[full-face diving mask]]. The [[Dräger P-port]] system with a [[bayonet connector]] is used on [[Dräger Panorama mask]]s, The Ocean Reef mask has a screw in connection, and the [[Kirby-Morgan 48 SuperMask]] uses a clip-on "pod" system

===Diffuser===
<!-- target for redirct [[Diffuser (breathing set part)]] -->
A diffuser is a component fitted over the exhaust outlet to break up the exhaled gas into bubbles small enough not to be seen above the surface the water, and make less noise (see [[acoustic signature]]). They are used in combat diving, to avoid detection by surface observers or by underwater [[hydrophone]]s, [[Naval mine|Underwater mine]] disposal operations conducted by [[clearance diver]]s, to make less noise,<ref name=CUMA /> to reduce the risk of detonating [[acoustic mine]]s, and in [[marine biology]], to avoid disruption of fish behavior.<ref name=aaus />

Designing an adequate diffuser for a [[Diving rebreather|rebreather]] is much easier than for [[open-circuit scuba]], as the gas flow rate is generally much lower.{{citation needed|date=March 2017}} An open-circuit diffuser system called the "scuba [[muffler]]" was prototyped by [[Eddie Paul]] in the early 1990s for underwater photographers [[John McKenney]] and [[Marty Snyderman]]; the prototype had two large filter stones mounted on the back of the cylinder with a hose connected to the exhaust ports of the [[Diving regulator#Demand valve|second-stage regulator]]. The filter stones were mounted on a hinged arm to float {{convert|1|to|2|ft|cm|sigfig=1}} above the diver, to set up a depth-pressure-differential suction effect to counteract the extra exhalation pressure needed to breathe out through the diffuser. The scuba muffler was claimed to cut the exhalation noise by 90%.<ref name="ep2007" /> [[Closed circuit rebreather]]s proved more useful in letting divers get near sharks.<ref name="wo2006" />