Setting a dive computer for altitude diving.

[Got2Go]

Leave it at A0...Or set it to A1 if you wish to add conservatism.
Its up to you and your comfort level/experience with your own diving (Ex: if you ride the NDL on your computer, then by all means, set it more conservatively).
And stay a minute longer at the safety stop, for additional conservatism.

There is very little difference from sea level to 700M...about equal to 0.8m of water depth.

 

[Tom_Ivan]

There is very little difference from sea level to 700M...about equal to 0.8m of water depth.

Cool! Thanks very much

 

[boulderjohn]

So lets pretend that I'm diving a lake that's at 650m. The A0 setting would give me the same bottom time up here as what it would give me at sea level. Am I right it saying that it would be considered dangerous to do a dive at sea level then immediately increase your altitude to 650m? Because this is essentially what I'm doing by starting at 650m.

The current DAN guidelines for flying after diving do not consider an ascent to that altitude as being a problem.

 

[Cr.padlo]

Many div e computers calculate your dives at sea level as they were at a higher altitude to add a level of conservation in nitrogen minutes. because the calculations are estimates, by increasing the conservation factor it increases the level of safety.

 

[yle]

So lets pretend that I'm diving a lake that's at 650m. The A0 setting would give me the same bottom time up here as what it would give me at sea level. Am I right it saying that it would be considered dangerous to do a dive at sea level then immediately increase your altitude to 650m? Because this is essentially what I'm doing by starting at 650m.

No need to get carried away. Atmospheric pressure at 650 m is about 94% of that at sea level. So the reduction in ambient pressure is measurable, but you can rest assured that the algorithms the dive computer uses take this difference into account.

That loss of 6% of atmospheric pressure is equivalent to the pressure of the depth of about 60 cm of sea water.

As for immediately increasing your altitude to 650 m... it really depends on how fast "immediately" is. The effect would be the same as ascending the last 60 cm of your dive. So how fast could you ascend that 60 cm and remain relatively safe? A few seconds? And there you go: ascending from sea level to 650 m in a few seconds (which would be a neat trick!) would essentially cause the same drop in ambient pressure (i.e. a difference of approximately 6%.)

I hope this helps to allay some of your concerns.

 

[HantsDiver]

So lets pretend that I'm diving a lake that's at 650m. The A0 setting would give me the same bottom time up here as what it would give me at sea level. Am I right it saying that it would be considered dangerous to do a dive at sea level then immediately increase your altitude to 650m? Because this is essentially what I'm doing by starting at 650m.

The algorithm is conservative enough that it doesn't really matter.

Now when you talk about dangerous no one can really say. People react differently on different days. But for most people it wouldn't make the slightest bit of difference.

If you ever get into technical diving you will realise how much algorithms differ. Some by a huge amount. However for the most part they will all get you out of the water safely.

Personally I wouldn't worry about it.