Dive Computer and Repetitive Dives

[eweingarden]

The answer to this question is probably very obvious, but I need to ask anyway. When I do repetitive dives over a few days, does the computer calculate how much nitrogen has been off-gased from my last dive on one day, until the next dive on the following day? If I were to go out in the evening to a low elevation (but greater than sea level), how would the computer know that I may have a greater level of off-gasing, than if I remained at sea level? Thanks.

 

[SailNaked]

Yes your computer always knows what your altitude is, and calculates as well as it can what your loading is. assuming your computer is on your wrist and not in a bag at the hotel.
and if it was in the bag, then you would be slightly less gassy than the computer thinks you are, and since you go with the more conservative number, the computer is still correct.

 

[rongoodman]

That's why the manuals often contain warnings about loosing that data if you have to change batteries.

 

[Mr Carcharodon]

The answer to this question is probably very obvious, but I need to ask anyway. When I do repetitive dives over a few days, does the computer calculate how much nitrogen has been off-gased from my last dive on one day, until the next dive on the following day? If I were to go out in the evening to a low elevation (but greater than sea level), how would the computer know that I may have a greater level of off-gasing, than if I remained at sea level? Thanks.

Some, maybe not all, computers read ambient pressure at the surface and take that into account in offgassing. So if you take the computer with you it will take the changes into ambient pressure into account. Of course reading the manual for your computer is important since they do not all work the same way.

 

[Damselfish]

Yes it keeps track from one day to the next (assuming the dive profiles and interval are such that the computer has not completely cleared.) If the computer takes your elevation into account while offgassing, and you don't have it with you, obviously it can't know about that. But I would say if you're not going high enough to worry about after diving to begin with, it doesn't make enough difference to matter if the computer is with you. It's just not that an exact a science. Unless you are doing a midnight dive followed by an early dawn dive you're going to have mostly offgassed by your dives the next day anyway, not 100% and the computer will probably still be counting down time to fly, but close enough.

 

[Mustard Dave]

The answer to the question is 'read the manual'. Not all computers continuously monitor altitude post dive, and as the OP doesn't say which computer he has, nobody can answer the question.

OP - what sort of altitude changes are we talking? Travelling to altitude after diving should be avoided.

 

[beanojones]

OP - what sort of altitude changes are we talking? Travelling to altitude after diving should be avoided.

Stressing this point is well worth it. A good number of people who end in chambers in Hawaii come from people who drive over the Pali or Like Like sightseeing.

Including some silly inside tenders, who work as tenders then drive over the mountains and come back later the same day as patients.

 

[eweingarden]

Mustard Dave:
I have no plans of leaving sea level. I used that example to try and understand how my computer keeps track of nitrogen off-gasing throughout repetitive dives. The computer is a Sherwood Wisdom 3. I'll have to go back and re-read the manual; maybe I missed it first time through.

 

[CT-Rich]

the computer will also miss a bunch of other stuff, beyond any sight-see it is not invited on. For example, it doesn't know your general health, how well you have been hydrating, how effective your circulatory system is. Also, it won't know what your BMI is. A lot of stuff can effect your susceptibility to getting bent, that is why the tables are modified from the Navy tables. How conservative do you want it?

Just an idle thought about getting DCS, not really trying to make a point in anyone direction (been reading about how the original charts were determined... kind of scary).

 

[diverrex]

the computer will also miss a bunch of other stuff, beyond any sight-see it is not invited on. For example, it doesn't know your general health, how well you have been hydrating, how effective your circulatory system is. Also, it won't know what your BMI is. A lot of stuff can effect your susceptibility to getting bent, that is why the tables are modified from the Navy tables. How conservative do you want it?

Just an idle thought about getting DCS, not really trying to make a point in anyone direction (been reading about how the original charts were determined... kind of scary).

Exactly, there is lots the computer doesn't know. If anyone thinks it represents a precise calculation of their individual situation they are sadly mistaken. Whether it calculates a minor change in elevation is the least of it. It's an algorithm calculation with certain statistical probabilities, not an actual measurement of the body which is also why some people fall on either end of the probability curve, some getting "undeserved" hits and others pushing the limits with no negative effects.