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Suunto D5 User Guide

Decompression algorithm

Suunto's decompression model development originates from the 1980s when Suunto implemented Bühlmann's model based on M-values in Suunto SME. Since then research and development has been ongoing with the help of both external and internal experts.

In the late 1990s, Suunto implemented Dr. Bruce Wienke's RGBM (Reduced Gradient Bubble Model) to work with the earlier M-value based model. The first commercial products with the feature were the iconic Suunto Vyper and Suunto Stinger. With these products the improvement of diver safety was significant as they addressed a number of diving circumstances outside the range of dissolved-gas-only models by:

  • Monitoring continuous multiday diving
  • Computing closely spaced repetitive diving
  • Reacting to a dive deeper than the previous dive
  • Adapting to rapid ascents which produce high microbubble (silent-bubble) build-up
  • Incorporating consistency with real physical laws for gas kinetics

The Suunto Fused™ RGBM 2 combines and improves widely respected Suunto RGBM and Suunto Fused™ RGBM decompression models developed by Suunto together with Dr. Bruce Wienke. (Suunto dive algorithms are a culmination of expertise and knowledge accumulated over decades of development, testing and thousands upon thousands of dives.)

In Suunto Fused™ RGBM 2 the tissue half-times are derived from Wienke’s FullRGBM where human body is modeled by fifteen different tissue groups. FullRGBM can utilize these additional tissues and model the on-gassing and off-gassing more accurately. The amounts of nitrogen and helium on-gassing and off-gassing in the tissues are calculated independently from each other.

The Fused™ RGBM 2 supports open-circuit and closed-circuit diving up to a depth of 150 meters. Compared to previous algorithms, Fused™ RGBM 2 is less conservative on deep air dives, allowing shorter ascent times. In addition, the algorithm no longer requires tissues to be completely free of residual gases when calculating no-fly times, thereby reducing the required time between your last dive and flying.

The advantage of Suunto Fused™ RGBM 2 is additional safety through its ability to adapt to a wide variety of situations. For recreational divers it may offer slightly longer no- deco times, depending on the chosen personal setting. For open-circuit technical divers it allows use of gas mixes with helium - on deeper and longer dives helium based gas mixes provide shorter ascent times. And finally, for rebreather divers the Suunto Fused™ RGBM 2 algorithm gives the perfect tool to be used as a non-monitoring, set point dive computer.


Suunto D5 does not have Trimix diving and CCR support.

Diver safety

Because any decompression model is purely theoretical and does not monitor the actual body of a diver, no decompression model can guarantee the absence of DCS.


Always use the same personal and altitude adjustment settings for the actual dive and for the planning. Increasing the personal adjustment setting from the planned setting as well as increasing the altitude adjustment setting can lead to longer decompression times deeper and thus to larger required gas volume. You can run out of breathing gas underwater if the personal adjustment setting has been changed after dive planning.

Oxygen exposure

The oxygen exposure calculations are based on currently accepted exposure time limit tables and principles. In addition to this, the dive computer uses several methods to conservatively estimate the oxygen exposure. For example:

  • The displayed oxygen exposure calculations are raised to the next higher percentage value.
  • The CNS% limits up to 1.6 bar (23.2 psi) are based on 1991 NOAA Diving Manual limits.
  • The OTU monitoring is based on the long-term daily tolerance level and the recovery rate is reduced.

Oxygen related information displayed by the dive computer is also designed to ensure that all warnings and displays occur at the appropriate phases of a dive. For example, the following information is provided before and during a dive when the computer is set to Air/Nitrox mode:

  • The selected O2%
  • CNS% and OTU
  • Audible notification when CNS% reaches 80%, then warning when 100% limit is exceeded
  • Notification when OTU reaches 250 and warning when 300 limit is exceeded
  • Audible alarm when pO2 value exceeds the preset limit (pO2 high alarm)

WHEN THE OXYGEN LIMIT FRACTION INDICATES THAT THE MAXIMUM LIMIT IS REACHED, YOU MUST IMMEDIATELY TAKE ACTION TO REDUCE OXYGEN EXPOSURE. Failure to take action to reduce oxygen exposure after a CNS%/OTU warning is given can rapidly increase the risk of oxygen toxicity, injury, or death.

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