Did my Vyper try to bend me??

[Last Man Standing]

I recently did a series of dives while on holiday. It was two mostly two divers per morning, with an hour to hour and a half surface interval between each. Everything went fine during the holiday, some of the profiles got a bit close to entering deco and I had to keep a close eye on the computer to try to avoid entering deco. I remember entering deco once during the week and immediately started to ascend, by the time I reached the safety stop at the end of the dive, the computer showed there were no deco penalties left to complete, just the 3 minute safety stop.

Imagine my suprise and horror when I downloaded the dives onto my pc using Sunnto Dive Manager, and the graphs revealed multiple deco dives and missed stops!!

Before anyone thinks I've misread the computer underwater, I can assure you I didn't! I've completed over 200 dives with this computer, probably half of those have been deco dives, so I'm very familiar with this computer and I can confidently make the following statements:

1. I only noted the computer entering deco once during the week.
2. On no dives did I go to the surface before the display showed that all stops (including safety stops) had been completed.

Going through the graphs, I have noted that only one dive shows the yellow triangular marker, which indicates the computer has entered deco. (does anyone know if this is generated by the computer or the diver manager software?)

Despite having appeared to miss deco stops on 4 dives during the week, missed stops ranging from 3 to 6 mins, at no time did the computer lock out.

I've searched through the Dive Manager index and finally found this explanation:

Dive Manager sometimes over or under estimates the decompression required for a dive. Use the Profile Graph window to study dives transferred into your logbook through a PC Interface. You'll notice that some dives show tissue saturation over 100% on the bar graph, meaning that decompression was required. But during the dive your dive computer remained in no-decompression mode the entire dive. Dive Manager sometimes reports that you surfaced too soon, when you know you did not. Here's why:
Your dive computer breaks the dive into time equal segments called samples. It records dive information in its memory once during each sample. The information recorded is valid for one instant of time, not necessarily for the interval as a whole. The longer the interval, the less likely that this accurately represents the whole sample.
Dive Manager can only know the information for one instant during each sample. It must guess what happened during the remainder of the time. For example, your dive computer records the maximum depth reached during each sample. If you change depth, that number misrepresents the whole of the interval. Dive Manager can only assume you spent the entire interval at the recorded depth
During a playback, Dive Manager reconstructs the dive computer's math model using information for each sample. It cannot download the exact status of the dive computer's decompression model because the dive computer does not keep that information in its memory. Dive Manager estimates what the calculations must have been based on information recorded for each sample. The closer it represents the interval as a whole, the closer Dive Manager reconstructs the dive computer's math model.
Correct estimates are more likely if your dive computer uses a short sampling rate. Set the sampling rate to a shorter duration, but take care to avoid running out of dive computer memory. Set the sampling rate in Transfer, Settings.

So that explains that then! I spent the week after my hols frightened to lift my toothbrush incase I got a bend!!!

[David]

question

how did you feel after your dives each day. Any days you felt not yourself.


David

[Scubee]

i had this a couple of years ago. I went to 1 min of no stop time, and it was all fine when I got out of the water. On download, it seemed I had missed 8 mins of deco, and I emailed Sven at Suunto. I can't find his reply, but it is all to do with the delay between what the vyper remembers, and what it tells you at the time.

As far as i remember, SDM recalculates, rather than remembers, the decompression schedule, when you down load. Because it is on a 20 second snapshot, it may show you as having missed deco.

If you change the interval in SDM, say, to 10 seconds, it will give you a different result - logically, in your favour.

Suunto were absolutely categoric in their response that what the computer tells you when you are underwater is accurate, what the SDM tells you is accurate but dependant on the sample rate.

One of the perils of diving close to limits!
HTH

[weazelz]

Originally Posted by Scubee

If you change the interval in SDM, say, to 10 seconds, it will give you a different result - logically, in your favour.

what she said. turning up the sample rate to 10s from the default 20s makes for a less lumpy graph in SDM too

[Scuttler]

Altenatively switch to a VR3

[RogerViking]

look i know what everybody says about the vyper i use one too but only in gauge mode when doing deco. firstly if you can, change the sample rate to 20 or 30...and becides you shouldent be pushing the puter to its limits they cant handle it. surface interval when doing many dives should be 2 hours min.
dont shoot me just my 2p.

[Scubee]

Originally Posted by RogerViking

look i know what everybody says about the vyper i use one too but only in gauge mode when doing deco. firstly if you can, change the sample rate to 20 or 30...and becides you shouldent be pushing the puter to its limits they cant handle it. surface interval when doing many dives should be 2 hours min.
dont shoot me just my 2p.

erm... the OP was doing no-stop diving.
The default sample rate on the vyper is 20 secs.

[RogerViking]

yep yes it is.
i still regard tables work best but computers are great but don't push them ...but hey would you trust your life to one?

i remember a thread a while back about one vypers readout sticking.

[nigelH]

Originally Posted by RogerViking

computers are great but don't push them ...but hey would you trust your life to one?

Would I heck...

<punches 1.3bar ppO2 into YBOD>
<jumps in water>
<comes back two hours later>

Last time I did a dive on tables was June 2004.
I had to look it up.

[fatlaz]

I never had any problems like that with my vyper but it did start to go scranny and when I ascended to 6m would turn itself off and on again at random. I know I hadn't any need to do any deco but hung around for a while just to make sure. It only really did this in stoney (?) but I stopped being a fan of it. My dive times were wiped in the middle and all sorts. I keep meaning to send it to suunto but keep forgetting

AFAIK the vyper is v. conservative anyhow and thankfully you are ok, it may still be worth dropping suunto a line to see what they say though.

HTH

Ben.