UWSojourner
Contributor
Then maybe its time you took a fresh look:
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Q. How close are 40/70 to VPM-B +3?
a/ nothing - diametrically opposed?
b/ almost the same?
c/ identical?
I pick B.
Well, I guess we've come full circle. It was statements like this that made me post here what appears below. It would be easy to "pick B" based on your chart because your chart is specifically designed to blur distinctions. Some of those distinctions appear below for a 240ft dive.
And the questions still stands for the profile below: What benefit is VPM-B providing at the cost of 30% more decompression stress?
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Just saw this post so I thought I'd show some dissimilarities that I see between VPM-B+3 and GF 60/75 for your chosen profile of 240ft 20min.
1. The heatmap below clearly displays the same supersaturation pattern that the NEDU study displayed. VPM's deeper stops come at the price of continued on gassing during those deeper stops. The result is higher supersaturations than the GF profile once the diver surfaces. That pattern was also displayed by the losing A2 profile in the NEDU study. In contrast, GF gets shallower quicker (as did the superior A1 profile in NEDU's study) and surfaces cleaner as clearly shown in the supersaturation heatmap.
2. The profile created by VPM-B+3 for this dive has 30% more supersaturation exposure once the diver surfaces and about 20% overall. The only credible explanation for why the shallow stop profile in the NEDU study was superior was that it produced lower total supersaturation exposure (sometimes measured by "integral supersaturation"). ISS measures both supersaturation pressures the diver is exposed to and the time period the diver is exposed to them.
A diver should ask what benefit is VPM-B+3 providing at the cost of 30% more decompression stress at the surface?
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Why did I use GF60/75? I took the total runtime of the VPM-B+3 profile (89 minutes) and matched it to a GF profile. The GF40/70 does not match the runtime. So I found that both GF40/80 and GF80/70 matched pretty closely. I took their average for comparison. The key is that when assessing similarities in deco methods, keep the runtime constant.
But you don't have to use GF60/75 for GF to display superior integral supersaturation patterns. GF10/89 (about as "deep-stop-ish" you can make GFs) still produces 16% lower integral supersaturation at the surface and 10% lower overall. A low GF of 40 or 50 seems more in line with the NEDU study though. GF's algorithm of time allocation just seems to more naturally reflect the findings of the NEDU study.
Those are some dissimilarities that I see.
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