Everything you need to know about the classic RGBM algorithm- reviews, safety, and settings.

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In the depths of the underwater world, our bodies experience an invisible but very real thermodynamic phenomenon. As we ascend towards the surface, the gases dissolved in our tissues seek to escape, sometimes forming silent microbubbles that circulate within our venous system. Most traditional algorithms attempt to manage this phenomenon by modeling only the tension of the dissolved gases. The classic RGBM (Reduced Gradient Bubble Model) algorithm developed by Bruce Wienke offers a different approach by actively simulating the physical behavior of these bubbles to prevent their growth.

I remember my early teaching dives at a dive school with a student using an old Mares computer that utilized the classic RGBM algorithm. During our buoyancy exercises and repeated ascents near the surface, his device proved remarkably conservative, imposing significant penalty times for decompression stops compared to mine. This experience demonstrated the protective but uncompromising nature of this two-phase model, which acts as a true safety net for divers who are still learning.

This algorithm is proprietary and closed-source. The exact code and calculation parameters remain protected by industrial patents, making it a "black box" for divers. Historically, versions and derivatives of the RGBM have been found in Mares products (Mares-Wienke RGBM) and Cressi products (particularly on the Leonardo and Michelangelo dive computers), which utilize this model for its high level of passive safety in recreational diving.

Ease of use is one of the major advantages of dive computers that use the RGBM. Designed for the general public, they eliminate the mathematical complexity of Gradient Factors in favor of very accessible settings options.The conservatism setting is configured through simplified personal parameters, typically labeled P0, P1, P2 (from least conservative to most conservative), or altitude settings A0, A1, A2. Simply choose your desired level of caution based on your age or fatigue before entering the water.

For dives using Nitrox or air, multi-gas management is seamlessly integrated. On Cressi or Mares models that support it, switching between tanks during a dive is done with a simple button press, and the computer instantly updates the total decompression curve.

The classic Wienke RGBM is a rigid mathematical model that does not account for actual biometric variations such as your heart rate or body temperature during the dive. However, it can be strict when dealing with risky behaviors. If the computer detects a rapid ascent, consecutive dives performed close together, inverted dives (a deep dive after a shallow dive), or "yo-yo" profiles, the algorithm immediately applies very significant penalties by reducing the no-decompression limit (NDL) or adding mandatory safety stops.Deep stops are at the heart of the RGBM philosophy. The algorithm requires short stops (often one to two minutes) at mid-depth to limit the physical expansion of microbubbles early in the ascent, before reaching the shallower depths of conventional decompression stops near the surface.

DAN statistics show that for recreational diving without decompression stops (within the safety profile), RGBM offers an excellent level of passive protection. Decompression accidents are extremely rare with this algorithm, precisely because of its inherent conservatism.

However, contemporary medical consensus has profoundly evolved regarding deep and technical diving. A major clinical study conducted by the U.S. Navy Experimental Diving Unit (NEDU) in 2011 demonstrated that the deep stops imposed by bubble models (RGBM/VPM) were actually ineffective and increased the risk of decompression accidents by forcing divers to remain at depth, which continues to saturate their slow tissues. For this reason, hyperbaric medicine now recommends prioritizing Haldanian models (Bühlmann) with shallow stops.

The major drawback is its excessive conservatism during repetitive dives, especially on dive trips (3 to 4 dives per day). The accumulation of simulated nitrogen by the algorithm can quickly and drastically reduce your bottom times compared to other divers in your group, which can be very frustrating.

In practice, if you are diving with a computer equipped with the standard RGBM (such as the Cressi Leonardo) alongside a buddy using a Haldanian algorithm (like a Shearwater or a Garmin), you will almost always be the limiting factor for the group. Your computer will display mandatory decompression stops much earlier than theirs, forcing you to shorten your dive.

To analyze the technical specifications of Cressi or Mares computers that use this technology, we invite you to consult our AquaExposure Dive Computer Comparison Tool, which centralizes all the actual specifications for each model.