[This is a post by Rick Walsh but this information got lost when this blog moved to a new server.] When I mentioned to one of my dive buddies I was considering taking a GUE Tech 1 course, his response was “I wouldn’t trust that ratio deco crud”. Another explained calculating ratio deco by: average the depth of your dive; double it; add the last two digits of the serial number of your bottom timer; divide by the number of divers in your team, which is always three; then subtract the number you first started with. For better or worse, there is a perception among many of us non-DIR (or not yet DIR) decompression divers that ratio deco is dangerous voodoo that should be avoided. But could it be justified?

V-Planner dive decompression planning software. V-Planner is a decompression program that uses the Varying Permeability Model for decompression profiles.The VPM-B decompression model is well suited to today's technical diving.

Let me state now that I have no training in ratio deco, have never used it myself, and I am not advocating its use. If you are interested in applying it to your diving, I encourage you to take a course that covers it and how and when it can be used, and most importantly its limitations. Do not take reading something on the internet as a substitute for appropriate training. This post is intended to discuss the concept of ratio deco far more than the practice. I mention GUE, but the concept applies just as well to other versions of “ratio deco”.

What is Ratio Deco? Ratio deco is a method for calculating or adjusting a dive decompression profile, which does not require referring to a decompression dive computer, tables or software. As such, the plan can be adjusted or re-calculated on-the-fly during the dive without relying on a dive computer’s decompression calculations. To many, that sounds too good to be true. 3d custom girl download. Almost all decompression software, dive computers and tables in current use are based on Buhlmann or VPM-B decompression models or some varient thereof.

These models have received theoretical and real-life testing, include calculation for sixteen different theoretical tissues, and permit unlimited combinations of dive depths, durations, breathing gasses. Surely this cannot be replaced by a new decompression model calculated on-the-fly by the diver. In science, engineering, medicine, and many other disciplines, there are countless complicated mathematical models that cannot be generalized by a simple function. However, by controlling some variables, the relationship between others become simplified.

It is possible to use linear approximations for non-linear functions over limited ranges with acceptable levels of accuracy. In reality, ratio deco is not a decompression model. Rather it is a series of approximate relationships and trends that can be observed from ascent schedules calculated using existing models. Searching the internet suggests GUE Ratio Deco is derived from either VPM-B with +2 conservatism, or Buhlmann with approximately 30/85 gradient factors. Either way, it is attempting to replicate a bubble model profile, so comparing it to VPM-B +2 is justifiable. Whether bubble models generally, or VPM-B specificaly, are the best choice of decompression model is another topic or much debate.