what does it do and what doesn't it do?

Okay, I know, I sound like an absolute dork asking this question, but, like Socrates once said: "The first step to wisdom is the recognition of ignorance" (or something of the sort):bonk:

So, waht i want to know is. What does a computer do for me and what does it not do?
I am not referring to extra's like integrated air, detection of microbubbleformationrisksituations, PC interfacewithcoollookingflashinglights etc.
I am referring to the basic, it does your tables for you kind of thing.
What I had assumed is that the computer tells you how much bottom time you have left, based on how much nitrogen there presumably is in your system. Most importantly I assumed that the computer does this taking into account not only the amount of time you have been on a certain depth on that dive, but also how much residual nitrogen there is left from any previous dive.
Is this true? Or is it only true for some computers and not others?

Does having a computer not necesarily mean I will not be doing tables again? For example if I do a dive, have a surface interval long enough to get to PG "B", and get into the water for a second dive, will my computer know I am a B diver going for a repetitive dive? Or will the computer just assume it is my first dive of the day?
Any help would be much appreciated!

Hi

Your dive computer (depending on brand but i use Suunto Vytec) will measure depth, temperature and time and then calculate how much no deco time or how much deco time is necessary for you to finish the dive safely within the limits of decompression algorithms etc.

If you imagine when you dive that you are constantly changing depth which is were a computer is better than tables. Your computer effectively checks tables for you every 10 seconds or so. It means that you will be able to stay down longer than the ultra conservative tables which you use assuming you spent all your dive time at the maximum depth which is not true.

After your dive your dive computer is still doing calculations checking your current tissue code and planning your next dive. They are fantastic for repetitive diving which is what you would do in Red Sea etc.

You can still use tables and I still do as part of dive logging.

A computer is also useful for determining your ascent speed and will warn you if you are ascending too quickly. Interestingly, when I stopped using tables and started using a computer my ascent speeds slowed right down. BSAC say that it should take 1 minute to ascend from 6 metres. That is really very slow.

I personally think everyone should dive on computer.


Kindest Regards

Andy

wetlettuce once bubbled...

I personally think everyone should dive on computer.

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Uh Oh, I think I can hear Uncle Pug lurking around the corner to jump on that statement with his famous "computers rot the brain".

computers can do all that and more but I do not agree that everyone should dive computers . computers are definately better than a half or not at all job at tables . Everyone certainly needs to keep track of their profile and how it is influencing your body .but some people feel that letting a dive computer do your thinking for you takes away half the fun and I am one of them . tables and bottom timers are not for everyone but nor are computers.
joens

You'll find lots of differences in the way folks use computers - from "not at all" to "nothing but."
Most recreational divers who buy a computer never look at a dive table again. That's not necessarily bad, given the kind of diving most recreational divers do, and so long as they are willing to take the consequences of a computer failure (end the dive, no more diving for 24 hours).
Personally, I run tables as a backup even on recreational dives. Not because I don't think the computer's good, but because I am *not* willing to lose a dive due to a computer failure. By running parallel tables I can just keep on diving.
Rick

I used to "back-up log" my dives and run a table on them afterwards, for exactly this reason.

However, I found that on a great many of my profiles after the first dive the second and subsequent dives that day, while WELL within the limits on the computer, were beyond the limits on the tables.

This is clearly due to the multi-level nature of a computer dive, and the ability of the computer to track actual time at a given depth, instead of the table-based maximum-depth computation, which overstates your nitrogen loading.

If the computer were to break in such a situation, my diving day is over anyway, since I cannot back into the tables in that situation. As such there is no way for me to safely continue diving until I have completely offgassed all accumulated nitrogen load.

I've stopped doing this simply due to the lack of utility of it as a means of backing up a computer failure.

Genesis once bubbled...
I used to "back-up log" my dives and run a table on them afterwards, for exactly this reason.

However, I found that on a great many of my profiles after the first dive the second and subsequent dives that day, while WELL within the limits on the computer, were beyond the limits on the tables.

This is clearly due to the multi-level nature of a computer dive, and the ability of the computer to track actual time at a given depth, instead of the table-based maximum-depth computation, which overstates your nitrogen loading.

If the computer were to break in such a situation, my diving day is over anyway, since I cannot back into the tables in that situation. As such there is no way for me to safely continue diving until I have completely offgassed all accumulated nitrogen load.

I've stopped doing this simply due to the lack of utility of it as a means of backing up a computer failure.

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I've been kicking this around in the back of my head for awhile too. Does anyone know a way to work around this problem, other than diving with a backup computer? Perhaps there is a way to convert the computer's remaining time to desaturation to a pressure group for use with tables/wheels?

djhall once bubbled...

I've been kicking this around in the back of my head for awhile too. Does anyone know a way to work around this problem, other than diving with a backup computer? Perhaps there is a way to convert the computer's remaining time to desaturation to a pressure group for use with tables/wheels?

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If your computer fails and you're out of limits (according the tables), the best thing for you is to finish your diving day.

Thanks for the info Andy,

The Red Sea situation is exactly the sort of thing I was thinking about. So not every computer does that but some do, great!

About the only using a computer thing; IMHO I think it's always a good idea to do the tables/wheel once in a while, just to remember how to do it. But, when DM-ing I would always do the wheel, because when there are divers in the group who do not use a computer but do use the wheel it could be weird if you ended up doing a dive beyond the limits of the wheel . Also if there are divers who don't do any planning and just follow your fins I would also do the wheel or maybe even the tables, just to encourage them to do the same. O well, thats just my two cents..

MonkSeal once bubbled...

If your computer fails and you're out of limits (according the tables), the best thing for you is to finish your diving day.

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Your computer calculates multi-level profiles based on hundreds of levels during the course of your dive, if I understand correctly. Tables treat the entire dive as if it occured at the maximum depth reached during the course of the dive. Unless you are making shallow dives to < 50 feet (where air limits are greater than the NDL) or are acutally diving true square profiles, won't your computer based dives always exceed the limits of your tables when calculated as square profiles?

I'm not suggesting I should just keep diving anyway. That would be stupid in the extreme. I'm just wondering how so many people talk about calculating their computer dives with table profiles for backup. I don't understand why they aren't off the limits of the tables becasue of the difference between multi-level and square profiles.