PADI tables vs TDI/USN tables vs Dive Computer

[Wibble]

All ancient relics. Including the algorithms which all disagree with each other. To be frank this includes the bubble models (VPM, RGBM, etc), ratio deco and deep stops.

With decompression diving it’s important to have proven, consistent and common results, especially when diving as a team. Hence the widespread adoption of Bulhmann with Gradient Factors (also known as ZHL16+GF). All proper dive computers support this along with the myriad dive planners, including some open source planners (Subsurface).

Few technical divers would choose the Suunto toys and would be very unpopular in a team as the ascent curves differ widely from Bulhmann and unnecessarily extend decompression times for all.

 

[Wibble]

You just need to cut a different set of PADI tables.

They will be sub-optimal for decompression diving because DSAT (PADI RDP) algorithm is supposedly using the fixed sea-level value for maximum allowed overpressure whereas in other models (based on empirical data) that value goes up with depth. As a result Buhlmann will generate shallower/shorter/fewer decompression stops; DSAT will generate unnecessarily long decompression schedules.

Fine 20 years ago when dive computers were in their infancy. Not nowadays where Bulhmann and proper dive computers are used.

 

[Hoyden]

When I took my instructor exam, when I did the work for a question using the wheel, I came up with an answer exactly in between 2 of the multiple choices. I did it again and again and again. I finally took a guess on one of the two and, of course, picked the wrong one. As required, the examiner went over my error with me, showing me with his wheel how to get to the correct answer. It worked. I then handed him my wheel and asked him to do it again. He got my wrong answer. That tiny difference in our wheels made all the difference.

Of course, the correct answer was "It just doesn't matter." In the real world, either answer was plenty close enough.

I had this exact same experience. I was already a tech diver when I did my IE and wow, I hated the the freaking wheel.

Jackie

 

[dmaziuk]

Fine 20 years ago when dive computers were in their infancy. Not nowadays where Bulhmann and proper dive computers are used.

The timeline is available at a google near you. ZH-L16 was published a few years before DSAT report. You might want to look up a dictionary definition of "proper" while you're at it: DSAT has been formally tested and validated for no-stop diving whereas ZH-L, to my knowledge, has not.

 

[tursiops]

With decompression diving

Not the topic here.

 

[Wibble]

Whatever padi says must be true.

For all others there’s Bulhmann, especially when going beyond RDP

 

[boulderjohn]

I must confess that I do not know too much about the details of the research Buhlmann did between 1959 and 1983, when his first work was published, but I suspect that there was enough research on NDL diving to make us all reasonably confident in the tables he produced for that and the computers that use Buhlmann for NDL diving.

 

[dmaziuk]

I must confess that I do not know too much about the details of the research Buhlmann did between 1959 and 1983, when his first work was published, but I suspect that there was enough research on NDL diving to make us all reasonably confident in the tables he produced for that and the computers that use Buhlmann for NDL diving.

In NDL diving you're limiting yourself by the surfacing M-value (M0), just like DSAT does, so the only differences you get are from the actual numerical differences in M0s and tissue compartment half-times. The end results are not identical but close enough for practical purposes.

 

[Wibble]

Was trying to remember what DSAT was. It's a PADI mob called "Diving Science and Technology" which developed the Recreational Dive Planner (RDP) beloved of PADI.

Must be better than Bullhmann as it was developed afterwards (standing on the shoulders of giants). Or maybe it's just a "special" algorithm that works for a small subset of diving conditions, rather than the more general algorithm developed by Bullhmann.

 

[tursiops]

Was trying to remember what DSAT was. It's a PADI mob called "Diving Science and Technology" which developed the Recreational Dive Planner (RDP) beloved of PADI.

Must be better than Bullhmann as it was developed afterwards (standing on the shoulders of giants). Or maybe it's just a "special" algorithm that works for a small subset of diving conditions, rather than the more general algorithm developed by Bullhmann.

I know you are just making your usual rant about how Bühlmann is better than anything else, but it is worth noting that the RDP was actually tested quite well with chamber and real divers, and was specifically optimized for recreational diving. Its development was concurrent with Bühlmann's later work, not after it. If perchance you want to actually see some history and facts on Bühlmann and RDP -- although it is more fun to rant in the absence of facts -- you should look at:
The DSAT Recreational Dive Planner, R. Hamilton et al (1994) (linked at Dropbox - DSAT_1994_unsecured.pdf - Simplify your life)
Deco for Divers, M. Powell (2016)
Deep into Deco, A. Salama (2015)