A dive computer or decompression meter is a device used by a scuba diver to measure the time and depth of a dive so that a safe ascent rate can be calculated and displayed so that the diver can avoid decompression sickness. Suunto Oy, based in Finland, is a company that produces and markets magnetic sports Compasses and other Navigational products along with various mechanical Scuba diving is swimming underwater, or taking part in another activity while using a Scuba set. Decompression sickness (DCS, the diver’s disease, the bends, caisson disease is the name given to a variety of symptoms suffered by a person ^[1]

Contents 1 Purpose 2 History 3 Display information 4 Audible information 5 Operation 6 Algorithms 7 Special purpose dive computers 8 Precautions 9 Manufacturers 10 Market Share 11 See also 12 References 13 External links

Purpose

Dive computers address the same problem as decompression tables, but are able to perform a continuous calculation of the partial pressure of inert gases in the body based on the actual depth and time profile of the diver. Dive Tables, Decompression Tables or Tables are printed cards or booklets that allow divers to determine for a particular dive profile and breathing gas In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume A dive profile is a two dimensional graphical representation of a dive showing depth and time ^[1] As the dive computer automatically measures depth and time, it is able to warn of excessive ascent rates and missed decompression stops and the diver has less reason to carry a separate watch and depth gauge. A decompression stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive to safely eliminate absorbed Inert gases from A watch is a timepiece that is made to be worn on a person The term now usually refers to a wristwatch, which is worn on the wrist with a strap or Bracelet. A depth gauge is a Pressure gauge that displays the equivalent depth in water Many dive computers also provide additional information to the diver, for example, the water temperature, information on the diver's oxygen toxicity or the pressure of the remaining breathing gas in the diving cylinder. Oxygen toxicity or oxygen toxicity syndrome (also known as the " Paul Bert effect" or the "Lorrain Smith effect" describes harmful effects caused Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Air is the most common and only natural breathing gas. Other artificial gases either pure gases or mixtures of gases are used in breathing equipment and enclosed habitats such A diving cylinder, scuba tank or diving tank is used to store and transport high Pressure Breathing gas as a component of SCUBA (Self-Contained

Because of the computer's ability to continually re-calculate based on changing data, the diver benefits by being able to safely remain underwater for longer periods of time using an equal volume of gas. For example, a recreational diver who plans to stay within "no-decompression" limits can in many cases simply ascend a few feet each minute, while continuing the dive, and still remain within safe limits, rather than adhering to a pre-planned bottom time and ascending directly. So-called multi-level dives can be planned with traditional dive tables, but the additional calculations become complex and the plan may be cumbersome to follow. Computers allow for a certain amount of spontaneity during the dive.

History

The Office of Naval Research funded a project with the Scripps Institute of Oceanography for the theoretical design of a prototype decompression analog computer. The Office of Naval Research ( ONR) headquartered in Arlington Virginia ( Ballston) is the office within the United States Department of the Scripps Institution of Oceanography (sometimes referred to as SIO, Scripps Oceanography or just Scripps) in La Jolla California, is one of the The Foxboro Decomputer, Mark I was manufactured by the Foxboro Company and evaluated by the US Naval Experimental Diving Unit in 1957. Year 1957 ( MCMLVII) was a Common year starting on Tuesday (link displays the 1957 Gregorian calendar) ^[2]

In 1965, Stubbs and Kidd applied their decompression model to a pneumatic analogue decompression computer. Year 1965 ( MCMLXV) was a Common year starting on Friday (link will display full calendar of the 1965 Gregorian calendar. ^[3][4]

The first recreational mechanical analogue dive computer, the decompression meter was marketed by Scubapro in 1972. Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment An analog computer (spelt analogue in British English is a form of Computer that uses continuous physical phenomena such as electrical mechanical It was very simple in principle: a waterproof bladder filled with gas inside a big casing bled into a smaller chamber through a calibrated porous ceramic cartridge (to simulate tissue in/out gassing), whose pressure was measured by a manometer whose graduation indicated decompression stops. Many techniques have been developed for the measurement of Pressure and Vacuum. The device was eventually nicknamed bend-O-meter.

Several analogue decompression meters were subsequently, some with several bladders for illustrating the effect on various body tissues, but they were sidelined with the arrival on the scene of electronic computers.

Early examples of recreational diving digital, electronic computers, from 1979, are the Hans Hass DecoBrain and Orca Edge. Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for Year 1979 ( MCMLXXIX) was a Common year starting on Monday (link displays the 1979 Gregorian calendar) Hans Hass (born January 23, 1919 in Vienna, Austria) is a diving pioneer and mainly known for his documentaries about Sharks

In 2001, the US Navy approved the use of Cochran NAVY decompression computer with the VVAL-18 for Special Warfare operations. The Thalmann Algorithm ( VVAL18) is a Deterministic decompression model developed by Capt ^[5]

Display information

Dive computers provide a variety of visual dive information to the diver.

Modern dive computers display the following information on a LCD:

• Current depth.
• Maximum depth reached on this dive.
• No stop time, the time remaining at the current depth without the need for decompression stops on ascent. A decompression stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive to safely eliminate absorbed Inert gases from
• Dive time, often measured from the end of the last longer surface interval.

Many dive computers also display additional information:

• Required decompression stop depth and time.
• Water temperature.
• Ascent rate.
• Dive profile (often not displayed during the dive, but transmitted to a personal computer).

Some computers are designed to display information from a diving cylinder pressure sensor, such as:

• Gas pressure. A diving cylinder, scuba tank or diving tank is used to store and transport high Pressure Breathing gas as a component of SCUBA (Self-Contained
• Estimated remaining time based on available gas and rate of gas consumption.

Some information is only shown at the surface to avoid an information overload of the diver during the dive:

• "Time to Fly" display showing when the diver can safely board an airplane.
• A log of key information about previous dives.
• Maximum non-decompression bottom times for subsequent dives based on the partial pressure of the gases in the tissue.

Audible information

Many dive computers have warning buzzers that warn the diver of events such as:

• Excessive ascent rates.
• Missed decompression stops.
• Maximum operation depth exceeded.
• Oxygen toxicity limits exceeded. Oxygen toxicity or oxygen toxicity syndrome (also known as the " Paul Bert effect" or the "Lorrain Smith effect" describes harmful effects caused

Operation

Modern dive computers are battery-powered computers within a watertight case. In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy These computers track the dive profile by measuring time and pressure. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface All dive computers measure the surrounding pressure to estimate the partial pressure of gases in the human tissue. In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume More advanced dive computers also include additional information into the calculations, for example, the water temperature or the diving cylinder pressure.

The computer then uses the profile and a decompression algorithm to estimate the partial pressure of inert gases that has been dissolved in the diver's tissues. In Mathematics, Computing, Linguistics and related subjects an algorithm is a sequence of finite instructions often used for Calculation Based on these calculations, the computer estimates when a direct ascent is no longer possible, and what decompression stops would be needed.

Examples of decompression algorithms are Bühlmann tables, the Multi-Tissue Model, the Varying Permeability Model, and the Reduced Gradient Bubble Model. Bühlmann tables are Decompression tables developed by Dr Albert Bühlmann, who did research into Decompression theory at the Laboratory of Hyperbaric The Variable Permeability Model or VPM is an Algorithm that is used to calculate the Decompression stops needed for a particular Dive profile. The RGBM is a Dr Bruce Wienke's Algorithm, based on Varying Permeability Model, that is used to calculate the Decompression stops needed for a particular

Many dive computers are able to produce a safe decompression schedule for dives that take place at altitude, which requires a slower ascent than at sea level, because the computers measure the atmospheric pressure before the dive. When divers travel before or after diving and particularly when they fly, they should transport their dive computer with them in the same pressure regime so that the computer can measure the pressure profile that their body has undergone.

Algorithms

Algorithms vary by model from each manufacturer but only a few algorithms have been developed. An algorithm used may also be a modification of an existing algorithm. When considering a dive computer, the main feature to consider is the algorithm that the air decompression limit monitor uses. If you’re unaware which algorithm the model that you’re considering to purchase uses, don’t purchase it until that is known. The subcontractors and child companies that make the dive computers market these under an array of brand names.

The algorithm used prevents you from getting decompression sickness (DCS). Decompression sickness (DCS, the diver’s disease, the bends, caisson disease is the name given to a variety of symptoms suffered by a person Diving scientists use known data that is recorded and averaged from previous divers to form an algorithm. Interpreted data that the computer receives is used against the algorithm to determine deco and no-stop times. An algorithm tries to account for magnitude of pressure reduction, repetitive exposures, rate of ascent, and time at altitude. Scientists may not be able to account for age, previous injury, ambient temperature, body type, alcohol consumption/dehydration, and patent foramen ovale when determining how to form an algorithm.

The newest dive computers on the market use:

• Mares: Mares-Wienke Reduced Gradient Bubble Model
• Pelagic: modified Haldanean / Diving Science and Technology Database
• SEIKO: Buhlmann ZHL-12 + Randy Bohrer
• Suunto: Suunto-Wienke Reduced Gradient Bubble Model
• UWATEC: Buhlmann ZH-L8 /ADT (Adaptive), MB (Micro Bubble), PMG (Predictive Multigas)

Special purpose dive computers

Some dive computers are able to calculate decompression schedules for breathing gases other than air, such as nitrox, pure oxygen, trimix or heliox. The RGBM is a Dr Bruce Wienke's Algorithm, based on Varying Permeability Model, that is used to calculate the Decompression stops needed for a particular John Scott Haldane CH ( May 3 1860 &ndash March 14 / March 15 1936) was a Scottish Diving Science and Technology (or DSAT) is a corporate affiliate of PADI and the developer of the Recreational Dive Planner. Bühlmann tables are Decompression tables developed by Dr Albert Bühlmann, who did research into Decompression theory at the Laboratory of Hyperbaric The RGBM is a Dr Bruce Wienke's Algorithm, based on Varying Permeability Model, that is used to calculate the Decompression stops needed for a particular Bühlmann tables are Decompression tables developed by Dr Albert Bühlmann, who did research into Decompression theory at the Laboratory of Hyperbaric Air is the most common and only natural breathing gas. Other artificial gases either pure gases or mixtures of gases are used in breathing equipment and enclosed habitats such Nitrox refers to any gas mixture composed (excluding trace gases of nitrogen and oxygen this includes normal Air which is approximately 78% Nitrogen Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the See Heliox (cryogenic equipment for another use of the word Heliox Heliox is a Breathing gas composed of a mixture of The more basic nitrox dive computers only support one or two gas mixes for each dive. Others support many different mixes. ^[6]

Most dive computers calculate decompression for 'open circuit' SCUBA where the proportions of the breathing gases are constant: these are "constant fraction" dive computers. A scuba set is an independent breathing set that provides a scuba diver with the Breathing gas necessary to breathe underwater during Scuba diving. Other dive computers are designed to model the gases in some 'closed circuit' SCUBA (rebreathers), which maintain constant partial pressures of gases by varying the proportions of gases in the mixture: these are "constant partial pressure" dive computers. A rebreather is a type of Breathing set that provides a Breathing gas containing Oxygen and recycled exhaled gas In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume

Precautions

The ease of use of dive computers, however, also exposes the diver to other dangers. Dive computers allow divers to perform complex dives with little planning. This may lead divers to exceed their competence and experience by relying too much on the computer rather than proper planning, discipline and monitoring.

Many dive computers have menus, various selectable options and various display modes, which are controlled by a small number of buttons on the front of the computer. The diver should become familiar with the control of the computer on a series of shallow and undemanding dives before relying on it for more challenging dives.

For safety reasons it is recommended that a dive plan should be established before the dive and then followed throughout the dive unless the dive is aborted. This dive plan should be within the limits of the decompression tables. Dive Tables, Decompression Tables or Tables are printed cards or booklets that allow divers to determine for a particular dive profile and breathing gas This increases the margin of safety, and also provides a backup decompression schedule based on the dive tables in case the computer fails underwater. ^[1][7][8] The main problem in establishing dive computer algorithms is that the gas absorption and release under pressure in the human body is still not completely understood. Furthermore, the risk of decompression sickness also depends on the physiology, fitness, condition and health of the individual diver. Physiology (from Greek grc φύσις physis, "nature origin" and grc -λογία -logia) is the study of the mechanical physical

A diver wishing to reduce the risk of decompression sickness can take a number of precautionary measures such as:

• Use dive computers with a conservative decompression model
• Use safety factors with dive computers (e. g. using a high altitude dive mode for a dive at sea level)
• Add additional deep safety stops during a deep dive
• Make a slow ascent
• Add additional shallow safety stops
• Have a long surface interval between dives

Many computers go into a "lockout" mode for 24 hours if the diver violates the computer's safety limits, to discourage continued diving after an unsafe dive. While in lockout mode, these computers will not function until the lockout period has ended. Other computers, for example Delta P's VR3, will continue to function, providing 'best guess' functionality whilst warning the diver that a stop has been missed, or stop depth exceeded.

Manufacturers

There are only a few dive computers manufacturers:

• Benemec[1]
• Citizen
• Cochran Undersea Technology[2]
• Delta P Technology[3]
• HeinrichsWeikamp[4] (Open source)
• HTM Sports: Mares[5] and Dacor[6]
• HydroSpace Engineering[7]
• Liquivision[8]
• Pelagic Pressure Systems: Aeris[9] and Oceanic[10]
• UWATEC[11] child company of Johnson Outdoors
• Underwater Technology Center[12]
• Seiko
• Suunto

Others are selling computers clones made by Seiko(Apeks, Cressi, Dive Rite, ScubaPro, Tusa, Zeagle) or Pelagic Pressure Systems(Beuchat, Genesis, Seemann, Sherwood) or Benemec Oy(A. ( is the core company of a Japanese global corporate group based in Tokyo, Japan. Open source is a development methodology which offers practical accessibility to a product's source (goods and knowledge Johnson Outdoors Inc ( produces outdoor recreational products such as watercraft diving equipment compasses and navigational products and outdoor clothing ( (more commonly known simply as Seiko say-co is a Japanese Watch company Suunto Oy, based in Finland, is a company that produces and markets magnetic sports Compasses and other Navigational products along with various mechanical P. Valves).

Market Share

Pelagic is currently the global market leader in dive computers. Suunto announced in December 2005 that they had manufactured a million dive computers.

Statistics of dive computer manufacturers by market share are welcome to be posted and updated here.

Dive computer market share worldwide estimates by brand as of May 2008:

• Suunto 31. Suunto Oy, based in Finland, is a company that produces and markets magnetic sports Compasses and other Navigational products along with various mechanical 6%
• Oceanic 27. 0%
• Aeris 11. 9%
• Uwatec 6. 6%
• Mares 5. 3%
• Cressi-Sub 3. Cressi-Sub is an Italian Manufacturer of scuba gear.It's the oldest Underwater diving company presently existing officially it dates back to 8%
• Sherwood 3. 5%
• Scubapro 3. 1%
• Genesis 2. 8%
• Tusa 2. 0%
• Aqua Lung America 1. Aqua Lung America is a Vista California US firm which makes scuba gear. 3%
• Seaquest 0. 8%
• Zeagle 0. 2%

See also

• Bühlmann tables
• Reduced Gradient Bubble Model
• Thalmann Algorithm
• Varying Permeability Model

References

External links

• Dive computer reviews by Scuba Diving magazine.
• Dive computer reviews I by DIVERNET magazine.
• Dive computer reviews II by DIVERNET magazine.
• Reviews index, of DIVERNET magazine.

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