Shearwater - Perdix

The "gold standard" for technical dive computers.

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15 Items

per page
Set Descending Direction

ZHL-16C, VPM-B, DCAP, DCIEM, VVAL-18M ... Does It Really Matter?

At the risk of annoying those who do have a preference for a specific decompression algorithm, the simple answer for most divers is NO the algorithm is not critical. There is no expert consensus that any one of the current crop of decompression algorithms is better than another. All of these algorithms used in dive computers and desktop table generation software, when set to their default conservancy values, will get you out of the water with an acceptable margin of safety. Among technical divers, the trend has been toward significantly deeper initial stops, based mostly on anecdotal reports within the community that some divers 'feel better' after such dives. Yet some experts feel deep stops may be counter productive, an example of the lack of consensus. Recently, the RGBM model has been called in to question by a legal action but it's not clear if the issue is with the algorithm itself or a specific dive computers' implementation. What we can say for sure is they are all imperfect representations of actual decompression in humans.

Numerous variants of ZHL-16C are very widely implemented in both sport and technical dive computers. For technical diving, versions of ZHL-16C that include user configurable Gradient Factor modifications are very popular because the GF values can be used to generate deeper initial stops. VPM-B dive profiles typically also have deeper initial stops, along with reduced time at shallow depths resulting in a 'smoother' profile. Some divers believe the reduced shallow depth stop times may be too short for lengthy VPM-B profiles; the VPM-B/E and VPM-B/GFS variations exist to address this concern. DCAP was developed for use by early extended range divers (today we call them "technical divers".) VVAL-18M is the basis for the modern US Navy Tables. DCIEM has been extensively tested by the Canadian military to ensure its applicability to cold water working divers. RGBM (basis for NAUI tables with its roots in VPM) and DSAT (basis for PADI tables) are most often seen in no stop required sport diving applications.

The practices of decompression are not exact, in many ways as much about skill as science. Much of what we do in decompression diving is based on empirical observation and experience, rather than having a basis in theoretical science. Dr. R W "Bill" Hamilton, the late co-developer of DCAP and whose research in decompression is widely acknowledged as having a key role in opening up recreational extreme exposure diving in the early 90's, was fond of the saying "what works, works." The most important safety factor is not the decompression algorithm you select, rather your skill as a diver and that you closely follow the recommendations of that algorithm and safe diving practices in general.



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