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Delta-P VGM Algorithm What you think ?

1779 Views 11 Replies 8 Participants Last post by  taylojonyd, 
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Just looking some opinions on the VGM deco algorithm that is on the VRX and an option on the VR3.
How does it compare to other algorithm ?
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Mark Chase
Capt Morgan said:
Just looking some opinions on the VGM deco algorithm that is on the VRX and an option on the VR3.
How does it compare to other algorithm ?
Click to expand...

They are all bollocks and this one is no different. Now doubt it will get you out of the water just as safely as all the others do or don't depending on how hard you push it.



What you relay want in a deco schedule is for it to be easily adjustable and easily understandable in case the computer you were using to figure it out goes tits up and leaves you to do the math.


For me I can just about get my head around GF deco so thats what i stick too. Not because its any better than anything else, but just because I can figure it out in my head if needs be.


Shearwater Pursuit GF and Ratio Deco for back up.



ATB

Mark
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HeBails
I dive with someone who uses it on his Sentinel and he really rates it.
He has tweaked it to mimic my 30/85 GF profile and it is good at knocking out the deeper micro stops and bringing them further up the ascent.
We're usually within a few minutes of each other on bigger dives although the VGM always has him a stop ahead of me for the 1st few minutes of the stop, as in he'll start his 18m stop a few minutes before mine for example

<edit> it is pretty tricky to tweak though. It won't let you set an equivalent GF but it will tell you what the equivalent GF is after you've spent 15 minutes faffing with Lo/Mid/High. As with all things VR it is maddeningly complicated
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A
so how does your friend set it?
spent ages tryin to get it to resemble anything approaching 20/85 and just gave up.
tbh i wish id bought an ostc instead
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nigelH
Paul Bailey said:
He has tweaked it to mimic my ...
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What is this fascination with making two computers agree? We all know they are, at best, a good guess at the processes involved and nothing more.
If one computer wants deep stops and the other wants longer at 6 and you dive them both then you have a better chance to stay out of the pot but nothing gives a guarantee.

My preference is to have two computers running different algorithms and I'll look at them both as advice and make up my own mind what to do.
Conservatism depends on my gas reserves and if I'm getting cold. It is something it is easy to call in the water but not a choice you can make before the dive. I just want a computer to tell me where it draws the bent/not bent line and, being a coward, I will stay well away from it.

Sorry. I've gone off on this one again. It just annoys me...
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HeBails
nigelH said:
What is this fascination with making two computers agree? We all know they are, at best, a good guess at the processes involved and nothing more.
If one computer wants deep stops and the other wants longer at 6 and you dive them both then you have a better chance to stay out of the pot but nothing gives a guarantee.

My preference is to have two computers running different algorithms and I'll look at them both as advice and make up my own mind what to do.
Conservatism depends on my gas reserves and if I'm getting cold. It is something it is easy to call in the water but not a choice you can make before the dive. I just want a computer to tell me where it draws the bent/not bent line and, being a coward, I will stay well away from it.

Sorry. I've gone off on this one again. It just annoys me...
Click to expand...
He has made his mimic mine Nigel so we're somewhere near each other on our ascents.
He dives a Sentinel and I dive a JJ with a Shearwater.
It's nice to know that as we pass 90m he won't be stopping, same at 85, 80 etc etc... as I head up to my 1st deep stop at about 65m
To me that seems pretty smart but then I'm not that smart to begin with so perhaps it isn't.
Also I don't give a hoot what other people are doing on their deco. Just me and (if there is one on the day) the person I am diving with.
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HeBails
ajmp said:
so how does your friend set it?
spent ages tryin to get it to resemble anything approaching 20/85 and just gave up.
tbh i wish id bought an ostc instead
Click to expand...
I'll point him in the direction of this thread and hope he can explain the voodoo that is attached to anything that comes out of Mr Gurr's Inventin' shed
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nigelH
Paul Bailey said:
He has made his mimic mine Nigel so we're somewhere near each other on our ascents.
Click to expand...
But... But... you're near one another because you choose to do the same stops.

One of the wonderful things about rebreathers is that you can bung in extra stops because you want to stay with your buddy because you only need a gas plan for bailout.
I still can't see why frigging the algorithm so you actually see the same numbers helps. The computer doesn't have you on a string pulling you up. A good computer is recalculating all the time to reflect the dive you did so if it thinks you need a stop it isn't doing it just to be awkward, it might just be a good idea.

Sorry it's just me and my 'who is in charge?' fixation with computers. I carry computers to give me an opinion on stops. It tells me not to go shallower than some depth based on its mathematical model. It does not actually tell me to go up just that it no longer sees a problem with my next selected depth.
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NotDeadYet
Or just use paper tables and stop worrying.
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HeBails
I should also have added that he wanted to eliminate some of the deeper micro bubble stops on the deeper dives that the Sentinel and VRX were throwing in so tweaked the algo to reflect a curve that he was happy with.
He had all of last year to work out what suited him best and this year to validate it.
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deepestandy
Paul is referring to me here and before we get in to all this I'd just like to validate it by saying that I don't disagree with anyone on this thread... All I will say is do what makes you feel good and suits the way you dive, so for me this means something like 30/85GF (which as Mark pointed out; I can wrap my head round gradient factors). With this in mind I then set about making the Sentinel/VGM mimic this. I did this with a bit of guidance from Al Wright to start with then tweaked it to suit me. This has two benefits 1. I feel good after the dive 2. I can ascend with my buddy which is sometimes necessary for our B/O planning.

On to setting VGM... To be blunt, dive with a computer running fixed GF's (OSTC MK2 set to 30/85) or a set of paper tables that you now work for you then just play with the stops until it matches the profile. Once you get your head round how the changes alter the profile you can be quite precise with the 'shape' of the deco, you do need to do lots of diving to validate the changes you made though. The last thing I will mention is that the VR algorithm is quite conservative so to achieve a 30/85 I had to actually set the deep and shallow stops to -5, with the mid stops at +5. Dont be affraid to play around with it, just make sure you have a second computer or paper tables.

Hope that makes sense!
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T
I've set the VGM on my Sentinel to match the VPM-B +3 on my X1, the stop depths & times are almost the same. The profiles match up better the deeper the dive, for 50m & shallower the VGM still requires a few more minutes as compared to VPM.
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