Nitrox course. What's the point?

[MichaelMc]

Don’t get me wrong computers are a marvellous invention, but I only need to scribble out a map of where I want to go and a plan how to get there and back. There’s something beautiful about simplicity that appeals to me.

Simplicity is good. I think you'll find a computer useful though. But you might have to venture off plan to see the benefit.

 

[ToneNQ]

Actually the risk is the opposite of how you describe it, instead of looking at a map and planning a route including an alternative and bringing the map with you, instead you head off with the smartphone in the blind hope the battery doesn’t die or the coverage doesn’t fail leaving you in the middle of nowhere lost.

The hope is not blind, hence when the computer is truly, absolutely essential, people have redundancy. People ensure the battery is charged, the firmware is updated, tissue logs are not inadvertently cleared. In the map example, coverage failure doesn't leave you lost, it leaves you exactly where you're standing. If you had the forethought to think about coverage you could've downloaded offline maps..

Risk is a factor of consequence and likelihood, no single method insulates you from both. Computers greatly reduce the likelihood and consequence by tracking your dive with second by second data samples. Analogue instruments are only as good as the frequency they are monitored. Accuracy of the dive profile is less, therefore to control the likelihood of DCS you must increase the conservatism of the dive plan. If the vis is great and the wreck is good and the gas is going well, I can add 5min of bottom time, or spend a bit longer in the bottom decks, without any increase in risk. With analogue gear that is not wise, I really must stick to the plan and hope everything holds for the next dive.

To be clear, I'm not suggesting any reason for you to change. I will suggest your reasons listed to not change are inaccurate but that has no bearing on your current methods.

 

[Angelo Farina]

No I don’t and could you please quote where I said I exclude the time to the first stop, my dives are planned from the surface which includes the decent and assent and all deco. Deco is calculated to include the decent, bottom time and assent.

You said that your reset the bezel of your watch before ascending, This means that the dive time to be inserted in the table is evaluated at that moment... Instead I reset the bezel only when I have reached the first deco stop (6m, usually) and I read the time to be entered on the table. So I include the ascent time in the dive time. How do you include it, if you reset the bezel before ascending?
See your post. Perhaps I did not understand exactly what you did mean... But to me, it seems that you are following the procedure described in the US NAVY manual, where the dive time ends at bottom, before the ascent.

Run time is the total time elapsed since leaving the surface. For the assent I reset the bezel on the bottom and when reaching the station for each stop

 

[Storker]

to me, it seems that you are following the procedure described in the US NAVY manual, where the dive time ends at bottom, before the ascent.

I read that as adding the time from the bottom to his first deco stop to his total bottom time, unlike most tables which stops counting bottom time as soon as you leave the bottom and depend on a minimum ascent rate to avoid excess ongassing.

To me, that looks like a decent way to avoid messing up by taking too long to ascend (ongassing on the way), and it would introduce some conservatism into the schedule. It still doesn't avoid messing up by failing to properly note max depth, though.

 

[tursiops]

Hard to beat a map.

You know, someday they will invent a fork, a thing to help you eat. I'll bet it will be a whole lot safer and easier than spearing everything with your knife.

 

[doctormike]

I've been away from SB. I'll try to answer your question above. If MOD is being calculated using depth then the salinity constant you refer to above must be used. I don't understand what you mean by "putting it in and taking it out". Here is the formula using depth (the constant is DPA):

MOD = ((ppO2 / fO2) - 1) x DPA

DPA = depth per atmosphere and is equal to 33 ft for salt water and 34 ft for fresh water using imperial measures.

Perhaps I didn't explain clearly.

The only way to for a MOD alert to use "depth" would be if it actually MEASURED your depth. Which it doesn't. The only way you can measure depth directly would be to use something like a marked line and use that for your calculations during the dive.

Your computer doesn't measure depth. It measures ambient pressure, which it then converts to a depth using that constant so that you can have it displayed on your screen, so you can know how deep you are. But that derived number is not what is used to determine your current PPO2, which is what you actually care about for ox tox purposes. PPO2=ATA x FiO2. No feet or meters in that formula.

So, theoretically, yes, the computer could work with a variable called depth that it would calculate from ambient pressure by taking into account the salinity constant. But after that, to see if you were over your PPO2 alert value, it would have to adjust the result by taking into account that same constant again to calculate the MOD with your formula ("putting it in and taking it out").

 

[Angelo Farina]

I read that as adding the time from the bottom to his first deco stop to his total bottom time,

Probably it is as you say, let's see if @mac64 provides a clarification.
My point is: if later you have to add the ascent time to the bottom time, what's the purpose of resetting the bezel at depth, before ascending, causing the need of remembering two numbers and to make the addition? I prefer not resetting the bezel at depth, and watching the total dive time, which already includes the ascent time, when I arrive at 6m (and I am not narched anymore)...
The procedure described by @mac64 still appears to me unnecessary complex, hence less safe.

 

[Angelo Farina]

It still doesn't avoid messing up by failing to properly note max depth, though.

Max depth is shown by the secondary needle of the depth gauge. This has never been a problem for old-style divers using tables with an analog watch and a mechanical depth gauge...

 

[Celt]

You said that your reset the bezel of your watch before ascending, This means that the dive time to be inserted in the table is evaluated at that moment..

I reset the bezel to time the assent, I’m not using navy tables, I’m using IDeco Pro. Bottom time is from leaving the surface till you start the assent. I posted an example. I have all possible run times on a slate, usually 3, if conditions are poor I’ll leave early. If conditions are very good I’ll stay longer.

 

[Celt]

You know, someday they will invent a fork, a thing to help you eat. I'll bet it will be a whole lot safer and easier than spearing everything with your knife.

That’s a ridiculous analogy. I could use a spoon. If I was to follow your thinking I would have to sit with my mouth open while a machine feeds me. I just don’t want to go that helpless