Scuba & Training

Diving Computers & the Deco Algorithms Babylon

When is time to choose your dive computer and/or decompression algorithm… the market is rich in options for both needs. Sometimes confusing and too technically explained.

The below descriptions are not to go deep into the decompression theories or dive computers settings but rather just to give you a quick, basic and clear (I hope) description of what to expect. For dive deco theory you can find tons of good information online and normally is explained (on different levels) during the basic & advanced technical courses too.

What Is an Algorithm used in Dive Computers?

In a simple words, a dive computer algorithm is a mathematical formula(s) used to calculate your diving profile in the safest (theoretical) mode taking into considerations some factors: depth(s) and time at that specific depth(s), gas mixture(s), cylinders pressure/volume, ascent rate and mandatory deco/safety stops, surface interval between dives, water temperature, physical fitness (heart beats per minute), diving conditions etc.

The main goal of a dive computer algorithms is to keep the risk of decompression sickness (DCS) to an acceptable level based on theoretical models as per the latest research in the industry and data (set up into the dive computer) from actual dives.

No dive computer or decompression algorithm will ever know exactly what is really going on into your body, if your data set up are correctly or if you fallow all the good practice recommendations before and after the dive!

Everything is just at a theoretical level!

But the future is already here so the science is with us: O’Dive Doppler technology is giving you the opportunity to do a real on-site N2 micro-bubbles measurements post dive and see, adjust and improve your Quality Index diving profile!

As you already might noticed, various dive computers are using various decompression algorithms which leads to slightly different diving profiles.

So… what are the theories behind the decompression algorithms?

Haldane Decompression Theory: 1908, used till 1980’s by US Navy air tables, outdated by now.

Bühlmann Decompression Algorithm: 1960’s. ZH-L, from Zürich (ZH), limits (L) followed by the number of tissue compartments (and other identifiers).

VPM – The Varying Permeability Model: 2000-2002, Erik Baker and Eric Maiken. Not much used these days.

  • The VPM-B/E model variation is for the extreme or extra long dives and exposures.
  • The VPM-B/FBO model variation (Fast Bail Out) is for the use with closed circuit diving and a bail out situation.
  • The VPM-B + GFS model combination (Gradient Factor Surfacing) produces another type of relaxed profile.

RGBM – The Reduced Gradient Bubble Model:

Is used more at a recreational level, not in technical diving. Is giving quite long and unrealistic conservative deco profiles.

DSAT – The Diving Science And Technology Model : developed by PADI for Recreational Dive Planner (RDP).

GF – Gradient Factor – is the latest trend in the industry (integrated into many technical diving computers) and is defining as: “GF are presented as a fraction of the maximum inert gas “supersaturation” or M-value that can be tolerated by each of the theoretical tissue types or “compartments” (ZH-16) considered by the Buhlmann model without resulting in DCS.”

In your dive computer settings you’ll find two values: GF Low and GF High:

  • Low defines the first decompression stop – Lower the number, deeper the first stop – Pyle)
  • High defines the surfacing value – The higher Gradient Factor value (GF Hi) determines the surfacing tissue supersaturation.

There are other algorithms (military & commercial) used in the diving industry but either outdated or not applicable for sport/technical scuba diving (Cochran – EMC-20H).

The above details are not to be taken as accurate 100% but just as basic reference. There are many variations of the presented algorithms, not scope of my presentation.

Diving theory is extremely complex subject with lots of pro and cons on all sides.

Few personal recommendations:

  • Do your research before purchasing a diving computer. I know the price (your budget) is the number one criteria, but look a bit further for your needs (present & future).
  • Try to understand the settings (and keep them updated as per your dive plan) & limitations of your dive computer. Read the manual, ask a professional opinion!
  • Set & Adjust your decompression algorithm based on YOUR profile and not on your buddies! Simply because a Gradient Factor set-up works (apparently) good on your buddy doesn’t mean necessarily that will work (good) for you too!
  • Keep in mind that not every dive is the same and not every day your body is the same (in fact, getting older and more “gnawed” day by day therefore attention must be increased into extending/improving the safety margins).
  • There is no perfect and guaranteed diving algorithm & diving computer. Therefore, accidents, including DCS might happened. If you want to be 100% safe, choose a good Netflix documentary and watch it on while relaxing on your sofa.
  • Same computers (same brand) with small different inside setting can give different diving profiles therefore buddy check should include the diving computer basic too.

Who knows, maybe in 10 or 20 years, the methods used today will be considered outdated and unsafe and other theories and devices will support our hobby. Till then, stick to what is good known and proved so far.

Stay updated with the latest news & research, be flexible in understanding and applying the science in your diving activities.

Keep training, keep exploring, stay strong & stay safe!


General Scuba & Training YachtDiver®

First Response – be prepared for the unexpected & unwanted moments

At T101®, we take safety very seriously and training in First Response is one of our strong points. We offer a wide range of First Response / Firs Aid courses under the highest standards and accreditation of two well known and reputable agencies:

Divers Alert Network Europe & First Response International

The well known Divers Alert Network is involved World Wide for over 30 years in diving insurances, research, training & education, being a point of reference in the entire diving industry (sport & commercial, military etc).

Sport – Professional – Club – Family DAN Europe Insurance

Divers Alert Network Europe: accredited by US Coast Guard, Italian Coast Guard, Finnish Boarder Guard, Italian Red Cross, Italian Carabinieri, Apnea Academy, VIT Germany, WASD Europe, LIFRAS Belgium, NOAA, Association of Diving Contractors International, Swiss Resuscitation Council etc

DAN Europe Basic Life Support
DAN Europe Automated External Defibrillator
DAN Europe Hazardous Marine Life Injuries
DAN Europe First Aid
DAN Europe Oxygen Administration

First Response International is part of the big family


which speak by itself about commitment to high quality standards in training, procedures, safety and modern educational approach.

First Response International: accredited by

US Coast Guard & OSHA

Workplace CPR/AED
Bloodborne Pathogens
Oxygen Administration
Adult & Child Emergency Care

FRTI Online / eLearning

All courses are ILCOR accredited and are also in conformity with Romanian Law 319 / 2006 .

Extra online support (Zoom/Skype), class theory review, practical hands-on with Demo & Real AED – mannequin – medical & DAN Europe O2 kit, written exams & post-course analyzing & debriefing.

*The First Response courses are compulsory for professional sport SCUBA diving instructors and highly recommended for all divers and non-divers (seaman’s, athletes, parents, workers etc).

All certifications are valid for two years after which renewal (refresh course) is required.

In these days, knowing a basic life support / first aid procedures is not a caprice but a real necessity. From an office to a shipyard work, family to outdoor activities, knowing BASIC procedures in providing first aid is extremely important.

T101® is DAN Europe HIRA 2 accredited as Operator & Instructor level.

For inquiries & training, please contact me at:

Stay safe & dive strong!


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Scuba & Training

European Standard EN250

European Standard EN250

Recent, pe blogul PADI Pros Europe, a aparut o notificare (o reamintire de fapt) a unor modificari in standardul “European Standard EN250” dintre care, cel mai important (in opinia mea) se refera la:

“An octopus rig is not a preferred option if the depth is greater than 30m or the water temperature is less than 10°C, instead an alternative fully independent system is advised.”

  • daca adancimea este peste -30m sau temperatura apei este sub +10degC atunci in locul octopusului este necesara o sursa complet independenta de gaz.

Cu toate ca pare a fi o abordare noua care va trebuii implementata de catre toti producatorii de echipamente si implicit va duce la modificari in standardele agentiilor recreationale… totusi ideea nu este noua deloc.

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ANDI International

Incepand cu anul 1999, ANDI International a fost prima (si singura) agentie de certificari scuba care a implementat necesitatea utilizarii unui RBS – Redundant Breathing System (impreuna cu Safeair®/Nitrox la nivelul de OWD).

Complementar, in anul 2005, UK Health and Safety Executive (HSE) emitea aceasta afirmatie: “It was shown that SCUBA single demand valve systems capable of meeting the breathing performance requirements of BS EN 250, cannot be relied upon to meet the same requirements when used as part of an ‘Octopus’ system”. Raportul RR341 se poate citi aici si aici.

Este adevarat, tehnologia construirii regulatoarelor (prima etapa in special) a avansat mult dar raman alti factori ce recomanda si impun necesitatea folosirii unui RBS in toate tipurile de scufundari (recreationale si tehnice).

ANDI recomanda urmatoarele configuratii (minime) de RBS in functie de adancime:

– 20 mtr  = 2 Lt

– 30 mtr 3 Ltr

– 40 mtr = 4.5 Ltr

*presiunea de incarcare a cilindrilor RBS: 200bar

De asemenea, alte recomandari sunt valabile, dar detaliarea lor face parte din cursurile ANDI corespunzatoare.

Pentru informatii suplimentare referitoare la cursurile ANDI, nu ezitati sa ma contactati.

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T101-Technical & Diving Ops®

updated: April 2021