Everything you need to know about the classic RGBM algorithm: Reviews, safety, and settings.

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In the intimate depths of the underwater environment, our body is subject to 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 classical algorithms attempt to manage this phenomenon by modeling only the tension of the dissolved gases. The classic RGBM (Reduced Gradient Bubble Model) algorithm by Bruce Wienke proposes a different approach by actively simulating the physical behavior of these bubbles to prevent their growth.

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

Developed in the 1990s by Dr. Bruce Wienke, a prominent physicist working at the Los Alamos National Laboratory in the United States, the RGBM is a bubble model (or two-phase model). Unlike purely Haldanian models like Bühlmann, which only calculate the tension of dissolved gases in tissues, the RGBM takes into account the free gas phase, that is, the physical formation and growth of microbubbles. Its primary goal is to keep these bubbles below a critical volume threshold.

This algorithm is of a proprietary and closed nature. 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 (Mares-Wienke RGBM) and Cressi (particularly on the Leonardo and Michelangelo computers), which utilize this model for its high passive safety in recreational diving.

The ease of use is one of the major advantages of computers that utilize the RGBM system. Designed for the general public, they eliminate the mathematical complexity of gradient factors in favor of very accessible settings options.

The conservatism is configured through simplified personal settings, typically denoted as 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 single button press, and the computer instantly updates the total decompression profile.

The classic RGBM model by Wienke is a rigid mathematical model that does not take into account real biometric variations such as your heart rate or body temperature during a dive. On the other hand, it is very strict when it comes to risky behaviors. If the computer detects a rapid ascent, successive dives performed close together, inverted dives (a deep dive after a shallow dive), or "yo-yo" profiles, the algorithm immediately applies very heavy penalties by reducing the no-decompression limit (NDL) or adding mandatory decompression stops.

Deep stops are at the heart of the RGBM philosophy. The algorithm mandates short pauses (often one to two minutes) at mid-depth in order to limit the physical expansion of microbubbles from the very beginning of the ascent, before reaching the area of conventional decompression stops near the surface.

The statistics from DAN demonstrate that for recreational diving without decompression stops (within the safety margin), the RGBM algorithm offers an excellent level of passive safety. Accidents related to desaturation are extremely rare with this algorithm, precisely because of its inherent conservatism.

However, the contemporary medical consensus regarding deep and technical diving has evolved significantly. A major clinical study conducted by the U.S. Navy Experimental Diving Unit (NEDU) in 2011 demonstrated that the deep decompression stops prescribed by bubble models (RGBM/VPM) were actually ineffective and increased the risk of desaturation 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 decompression stops.

The main advantage of the classic RGBM is its optimal passive safety for beginner divers or those who lack buoyancy control, acting as a reliable safety net underwater.

The major drawback is its excessive conservatism during successive 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 the group, which can be very frustrating.

In the water, if you dive with a computer using the standard RGBM algorithm (like 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 sooner 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.

The classic RGBM algorithm remains a good option for occasional or beginner divers who are looking for maximum safety without complicated settings. Although its deep-stop philosophy is now considered outdated by the scientific community for decompression dives, it remains an excellent passive safety tool for typical recreational diving. Stars in their eyes.