May 2006

Vol. 21, No. 5     What's this?

Computers That Properly Penalize Reverse Profiles

from the May, 2006 issue of Undercurrent  

As the research study points out, some dive computers treat forward and reverse profiles identically, a very risky prospect for a diver who intentionally — or unintentionally —- conducts a reverse profile dive. We contacted Dr. Bruce Wienke, who developed the RGBM algorithm used by many computers. He told us:

There are a bunch of computers out there with my RGBM algorithm that do NOT treat forward and reverse profiles the same. They penalize recreational air diving slightly if reverse profiles are less than 30 fsw and depths are less than 120 fsw. Beyond that, bubble mechanics kicks in, that is, effects of excitation and growth of bubbles assumed in the model impact the diver staging regimen more notably.

Computers that do NOT treat forward and reverse profiles the same are:
• Suunto RGBM sets (Viper, Vytec, Stinger, D9, etc)
• Mares RGBM sets (M1, Darwin, Nemo, etc)
• HydroSpace RGBM Explorer,
• Zeagle RGBM Cobalt
• Steam Machines RGBM Rebreather Computer Controller
• Underwater Technologies Center RGBM UDC message-deco communication computer system

These computers will penalize reverse profile dives in no decompression limits and deco time/stop depths. Penalties increase with depth, and increment of the reverse profile over the earlier dive, but are time-modulated over roughly a four hour period. The penalties are incurred on air, nitrox, heliox, trimix, or constant ppO2 rebreathers.

RGBM software on the market (GAP, ABYSS, Explorer Simulator) all do the same thing.