Necessity of a back up computer/watch for NDL diving

[MaxBottomtime]

Only true if you are doing square profiles or really trivial multi-level dives.
Perhaps YOU are doing square profiles. Fine. Few do.

Perhaps you should warn the thousands of DIR and UTD divers who apparently don't know as much as you do.

 

[outofofficebrb]

Almost all of my diving is vacation diving - sometimes resorts, but most often liveaboards 7-14 nights in length where it's all repetitive diving, 4-5 dives a day. I am usually gone for 3-4 weeks at a time. I spend a lot of time and money to get there and missing dives or sitting out dives because of a failure, low battery is unacceptable and having to use tables and a bottom timer does not interest me. I think if you weigh the risk vs reward as others have mentioned, you will see what works best for you.

I don't bother with a backup with local diving.

 

[TMHeimer]

As mentioned, on most of my dives (very shallow) I only take the watch. A little less fussy when it comes to rinsing afterwords, and the watch costs maybe $30. Maybe that's a viable reason some people don't dive with two DCs?

 

[tursiops]

Perhaps you should warn the thousands of DIR and UTD divers who apparently don't know as much as you do.

LOL. Depth-averaging for N2 uptake/off-gassing is a cult not based in science but rather in fantasy. It is a rough approximation that works in restricted circumstances....kind of like saying PI is 3 or that Celsius is about a third of Fahrenheit, or that the NDL for air is 120/Depth (ft).
Yes, they've been warned, but they prefer to test the limits and live on the edge, just hoping that awful day does not come.... (/sarcasm)

 

[dmaziuk]

As mentioned, on most of my dives (very shallow) I only take the watch. A little less fussy when it comes to rinsing afterwords, and the watch costs maybe $30. Maybe that's a viable reason some people don't dive with two DCs?

I actually take the computer on these because I want the dive in my log, and my log is Subsurface.

 

[barth]

LOL. Depth-averaging for N2 uptake/off-gassing is a cult not based in science but rather in fantasy. It is a rough approximation that works in restricted circumstances....kind of like saying PI is 3 or that Celsius is about a third of Fahrenheit, or that the NDL for air is 120/Depth (ft).
Yes, they've been warned, but they prefer to test the limits and live on the edge, just hoping that awful day does not come.... (/sarcasm)

How accurate do you think a dive computer is? I guess from every 3 divers one has a pfo. A lot of things have impact on your “ndl”. (Water temperature, electric heating, body fitness, stress, work during the dive, dehydration and more.)

Actually your dive computer is also a rough
approximation that works in restricted circumstances....

Most of the time a diver surface without problems. But even if you do what your dive computer tells you, you can still have dcs.

 

[tursiops]

How accurate do you think a dive computer is? I guess from every 3 divers one has a pfo. A lot of things have impact on your “ndl”. (Water temperature, electric heating, body fitness, stress, work during the dive, dehydration and more.)

Actually your dive computer is also a rough
approximation that works in restricted circumstances....

Most of the time a diver surface without problems. But even if you do what your dive computer tells you, you can still have dcs.

I do not disagree. But I'd rather start with the best answer I can, instead of a bad guess based on somebody's unscientific assertion.

 

[dmaziuk]

 

[TMHeimer]

I actually take the computer on these because I want the dive in my log, and my log is Subsurface.

I log each dive by using the analog stuff and just remembering stuff like bottom temp., viz, bottom time. I write it all down in between the 2 dives and after #2 (dive, that is). Admit your way is a little easier.

 

[Joneill]

How accurate do you think a dive computer is? I guess from every 3 divers one has a pfo. A lot of things have impact on your “ndl”. (Water temperature, electric heating, body fitness, stress, work during the dive, dehydration and more.)

Actually your dive computer is also a rough
approximation that works in restricted circumstances....

Most of the time a diver surface without problems. But even if you do what your dive computer tells you, you can still have dcs.

I'd say a good DC set up correctly is the most accurate source of data you have before, during and after a dive.

However, as many have stated, there are other factors one should be considering in order to dive safely and avoid DCS and none of those other factors diminish the value of the DC data - rather, they supplement it.

I'm not really clear why you mention a PFO as that really has nothing to do with the value of a computer or not (or the need for a backup as the OP was asking about). The risk of DCS due to PFO is not even clearly established so not sure why it's relevant in this discussion?

Alert Diver | PFO and Decompression Illness in Recreational Divers