RGBM — What It Is and Why It Matters
RGBM (Reduced Gradient Bubble Model) is a decompression algorithm developed by Dr. Bruce Wienke that models both dissolved gas and free-phase gas bubbles. Unlike pure dissolved-gas models like Bühlmann, RGBM attempts to account for the formation and behavior of micro-bubbles in tissues, which some researchers believe play a role in decompression sickness even within no-decompression limits.
RGBM is used in some Mares and Suunto dive computers. Its defining characteristic is that it penalizes certain dive behaviors — like rapid ascents, yo-yo profiles, reverse profiles, and short surface intervals — by reducing subsequent NDLs more aggressively than a pure Bühlmann model would.
Frequently Asked Questions
Is RGBM more conservative than Bühlmann?
Not necessarily across the board. RGBM and Bühlmann compute limits differently, and their relative conservatism depends on the specific dive profile. RGBM tends to penalize repetitive dives and reverse profiles more heavily, while Bühlmann with low gradient factors can be equally or more conservative overall.
Can I switch between RGBM and Bühlmann?
Only if your dive computer supports both algorithms. Most computers run one algorithm exclusively. A few models, like certain Suunto units, use a proprietary RGBM variant without offering an alternative. Shearwater uses Bühlmann with optional VPM-B.
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