Quote: (Originally Posted by
dive2dive2000)
I know what a graph does and how to use one topside on a simulator or when running dive profiles
You said you did not like the computer because it was way to conservative(and I agree that's why I traded mine...), So how does a graph that is to conservative help you when running profiles
and how do you use it underwater?
No, I said that the VPM algo in the computer is vastly too conservative. Thank God I found out before I popped for the "upgrade".
I don't dive it in VPM mode for that reason. I dive it in Bulhmann (well, its approximation anyway) mode set to zero conservatism.
Quote:
I do deco from tables with a fixed bottom time, and a fixed run/stop time at various depths while ascending. How does a graph help you underwater is this info next to the graph? Please elaborate on your technique or if I am misunderstanding you please explain
And you always have exact fixed bottom times and exact depths as planned? I didn't think so; neither do I.
What I did when I got my VR3 was dive the computer right to the edge of what it thinks is "no deco", surface on its schedule, then observe and log how I felt. Then I "backed off",
using the tissue graph to guide me, until I felt great. This took me about a dozen dives in total to "calibrate" it to my personal physiology.
I then challenged that with a light
decompression dive, to validate that I still feel great. Yep. Over a bit of time I worked my way up to being willing to trust what I had learned about the graph and how it relates to
how I feel after I get out of the water on more serious dives.
That's really no different than how you approach using a new land-based computer package for the same purpose. When I first bought VPM/B I didn't immediately "trust" it for a big decompression dive without checking out how I felt after using it in far less serious exposures.
Today, I'm comfortable using the VR3 this way as my primary decompression tool. I still carry a backup bottom timer and a "quickie table" (just stop times from 10' on down) for anything with planned deco, because things DO break and having no depth gauge, timer or deco info with a nice obligation would suck. But you need the redundant bottom timer of some sort anyway, and the backup table is just a short sequence of numbers.
In the ocean (where I do nearly all of my deco diving) I generally try to keep runtimes to an hour or so for logistical reasons in most cases (I'm willing to go up around 90 minutes if I have great conditions and better-than-average surface support), so I wouldn't call the diving I'm doing with it today "extreme", but 30ish minutes of deco time is typically regarded as fairly significant and plenty to bend you good if you do it wrong or blow it off.
You
can't do this padding tables, because exactly what that modification of a given schedule does on any given dive is not deteminable from your past experience (unless you do the EXACT SAME dive the second, third, Nth time) since the dive times and depths are always a bit different. Further,
behavior matters - if you are somewhat slower (or have some sort of issue where you are momentarily above your target ascent rate, etc) there's no real way to accurately compensate for that on a table - but a computer can and does.
The interesting thing is that when I go pull the profile I actually performed after I am done and compare it against a VPM/B table post-dive, it matches
quite closely. But - I can't compute that VPM table on the fly while in the water as my laptop isn't depth-rated, and the only VPM implementation currently available in a computer is the VR3s, which I refuse to use because its stupid-conservative.
In other words, what I've figured out how to do is get a profile that looks a lot like VPM/B, dynamically computed and with the proper amount of conservatism
for me, while using the straight Buhlmann VR3, by using the tissue graph display.
The bottom line is that it works well for me. A "numeric/text" display computer simply can't give you the tools to perform this sort of shaping of the decompression curve in real-time; you need the tissue graph to do that.