Reference or Backup mode?

[lowviz]

Interesting. I took a look at the manual, http://www.vr3.co.uk/downloads/manuals/2007 VR computers manual.pdf

If you ascend beyond your deco stop for more than 60 seconds, the computer displays the directive "USE TABLE", but will continue to try and provide a best guess decompression algorithm. (By deco stop, I mean a real ascent ceiling, not a microbubble stop).

Based upon my playing around with VPM, this would mean greatly extended shallow stops, much longer than the original total ascent time.

Has this been your experience?

http://www.vr3.co.uk/faq/faq.php#37

RE violating a suggested deco stop:

Yes, I often take it on 'tables' dives. Ironically, it whines about my behavior and suggests that I use tables. However, it will let you do a second, third, etc. dive. Just keeps on complaining but offers valid info. Not user-friendly layout, but finally starting to love it. Nice to be able to blow off a planned gas change for back-gas if I have it. (I can be cheap)

Interesting observation about shallow stops, will be fun to test...


edit:
Just to be explicit, I think we both agree that stops aren't being missed, just taken at different depths/times. Your question (as I read it) is how much am I being penalized for forcing my computer to follow a different, but still 'safe', algorithm. Very interesting indeed.

 

[Charlie99]

When it starts whining and suggesting that you use tables, will it give a stop length for your current depth, or does it keep telling you to descend back to what it had previously calculated as the ceiling?

I do see how it could come up with some NDLs after an SI, but if it continues to run the VPM algorithm it will be assuming relatively large bubbles and would have very short NDLs.

It's an interesting challenge in product/feature definition.

Somewhat related, but in the opposite direction of conservatism, I've often wanted a computer where I could, towards the end of a dive, crank up the conservatism arbitrarily to the point where it generated the time to ascend that I had already decided to implement. I have done this with VPM and it does what I want, which is to generate an "ideal ascent" profile of the desired length, even if I don't have what would be considered a deco obligation with normal conservatism.

What would work for BoulderJohn is similar, but cranking the algorithm more and more liberal until his desired profile no longer violates the computer.

 

[lowviz]

When it starts whining and suggesting that you use tables, will it give a stop length for your current depth, or does it keep telling you to descend back to what it had previously calculated as the ceiling?...............

It keeps telling you to descend. However, IIRC, holding the violation depth long enough will get you back on track. Odd, but now I see that I only pay really close attention to what is running my current dive: tables or computer -not both. I need to work on this. When I'm playing with tables, the computer just comes along so I can get an easy final dive without grinding through multiple sets of tables.

...............Somewhat related, but in the opposite direction of conservatism, I've often wanted a computer where I could, towards the end of a dive, crank up the conservatism arbitrarily to the point where it generated the time to ascend that I had already decided to implement. I have done this with VPM and it does what I want, which is to generate an "ideal ascent" profile of the desired length, even if I don't have what would be considered a deco obligation with normal conservatism.................

Yes, that would be an extremely valuable option for terminating a dive gone bad. Send that suggestion to VR Technology. I clearly see the value.

 

[lowviz]

OK, it came to me -had to think about one of last year's dives. The VR-3 displays the original intended times (this will sound a bit weird) but it takes substantially longer than the displayed time to clear each stop. So you don't know how long it really is to the surface. But the VR-3 will get you home and even allow subsequent dives.

Now I really like your suggestion.


edit:
Forgot to tell you I have it set to BUH, not VPM:

"When BUH is selected decompression will be calculated using our standard modified Buhlmann ZHL 16 algorithm with 2 minute deep stops."

-I like the "our standard modified" part...

 

[Kevrumbo]

All my decompression diving has been based on either ratio deco or V-planner, so I have close to no experience with technical diving computers. I hope this is not too easy a question.

I recently did several technical dives with a buddy who was playing with a new computer. Our dives were planned using V-Planner, and we used bottom timers/watches for measuring devices. He had a new tech computer he wanted to play with, though, so he tried playing with the settings to see if he could come out reasonably close to what we had planned, and he wore it during the dive to see what would happen. Since he had no dives planned for a while after that, he did not care if it locked up.

As the dive progressed and we followed our ascent plan, the computer got increasingly cranky about our failure to follow its directions, even though our plan was really not all that different. During our 20 foot stop it got so angry it stopped advising us and went into error/gauge mode.

It got me wondering about something.

Are there any computers that have what I would call a reference mode or a backup mode? the idea of such a mode would be that the computer is a designated backup to the primary means of planning the dive. It could be the team wanted to use tables but liked the idea of having a computer backup, especially in case that unforeseen circumstances led to them having to deviate enough from their original plan that the tables they cut were too far off for comfort. It might be that the team is using computers but has designated one of the as the one to follow so that they can stay together on stops if the computer does not agree.

Maybe the only question I am really asking is if there are computers that won't lock up if you are not following them.

V-Planner S/W for the Liquivision X1:

. . .No lockouts or Use Table errors. . .V-Planner Live uses the same model settings and conservatism levels design as the desktop version. If the diver plans and carries out the dive in exactly the same manner as planned, then the dive run times are a perfect match. Or the diver can choose to do a multilevel, or just wander around as he/she feels like. In all cases, the ascent is re-calculated continuously every few seconds, and the latest ascent limitations are displayed.
V-Planner Live VPM-B, VPM-B/E dive deco computer firmware