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

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In the history of diving equipment, certain technologies leave a lasting impression due to their rigor. The historical Suunto RGBM algorithm, which equipped entire generations of Finnish dive computers, undoubtedly belongs to this category. Renowned for its inflexible conservatism and flawless protection, it has ensured the safety of millions of recreational divers while sometimes causing frustration during consecutive dives.

I remember my instructor dives in the cold waters of the North Sea with a student using a Suunto Zoop Novo running this historical Suunto RGBM algorithm. Although we meticulously followed our ascent rate, his computer severely tightened its safety stops after our second consecutive dive, forcing us to wait in the cold long after our fellow divers had surfaced. This dive reminded me of the protective but uncompromising nature of this historical algorithm, designed not to take any risks with the physiology of the diver.

From a modeling perspective, it is a bubble model- or two-phase model. It simulates both the saturation of dissolved gases in nine theoretical tissue compartments and the physical behavior of circulating microbubbles. It's essentially a "black box" where the exact source code and penalty coefficients remain Suunto's exclusive intellectual property. This algorithm has been used in most of Suunto's classic dive computers, from the entry-level Zoop Novo and Vyper Novo series to the D series (D4i, D6i, D9, DX) and the early generations of EON.

One of the strengths of this algorithm is its ease of use underwater. Suunto designed its menus to prevent divers from having to deal with complex concepts such as the Gradient Factors used in the Bühlmann algorithm.The conservatism settings are configured through very clear personal adjustments, often named P0, P1, and P2 (from standard to most conservative), along with altitude parameters A0, A1, and A2. Simply select your desired safety level in the menus before diving.

The algorithm handles Nitrox and recreational air very well. On models that support it, gas changes underwater during ascent are performed through intuitive button controls, with the processor instantly recalculating the total ascent time automatically.

The classic Suunto RGBM is a purely mathematical model that does not take into account direct biometric data in real time, such as the diver's heart rate or breathing effort. However, it closely monitors your diving behavior. If the computer detects a rapid ascent, "yo-yo" dives, or an excessively short surface interval between successive dives, the algorithm immediately applies severe penalties, reducing the no-decompression limit (NDL) or adding mandatory decompression stops.The model also incorporates deep stops- ranging from one to two minutes- at mid-depth, designed to limit the expansion of venous bubbles before the final ascent. On recent models equipped with this feature, divers have the option to disable these deep stops in the menus, retaining only the standard safety stop of three minutes at five meters.

Statistical data from DAN confirms that computers equipped with the Suunto RGBM algorithm exhibit an extremely low rate of decompression accidents. This exceptional level of safety stems from the inherently conservative nature of the algorithm, which effectively protects recreational divers against profile errors or physical fatigue.

However, modern medical consensus has distanced itself from the philosophy of mandatory deep stops for decompression diving. Studies by the Navy Experimental Diving Unit (NEDU) have shown that stopping too deep continues to saturate slow tissues with nitrogen, increasing the overall risk of desaturation. Aware of these developments, Suunto gradually evolved its models towards the Fused RGBM 2 before adopting the Bühlmann model with Gradient Factors on its latest generation devices.

The major weakness is its excessive conservatism during successive or intensive dives, such as those on liveaboards. Doing three dives per day with this model can quickly become restrictive, as the device drastically reduces bottom times compared to divers using computers from other brands.

In the field, a diver equipped with the standard Suunto RGBM will almost always be the "pace-setter" of the group. They will often be the first to start their ascent and perform the longest decompression stops, forcing their dive buddies who are using more permissive algorithms to follow their decompression profile.

To compare this classic Suunto model with newer technologies, we suggest using our AquaExposure dive computer comparison tool to evaluate the differences in scores and features.