Why no accurate computers?

[Happy Spearo]

@Barnaby'sDad- I have that cert and understand that would extend my time. However, if my tables say I can stay longer then my computer on air at a certain depth, I am sure the tables are going to say I can stay longer with Nitrox at a certain depth then my computer on a Nitrox setting. Same problem with conservatism in the computer. I still lose out time and now I paid more for Nitrox. : )

 

[Gareth J]

@Happy Spearo

Have you confirmed how your computer compares to the table over a dive series.
What you loose on the first dive you may well gain on the subsequent dive.

You are also suffering from the American problem of being restricted to no-stop dives. Most of my students would just do the bottom time and then do the required stops (as long as the dive passed the gas planning requirements)[1]. If they didn't want the punishment (the stops), they would shorten the dive.

I have already said, it is bad practice to mix and match. You either use tables, with the advantages and disadvantages, or computers with their advantages and disadvantages.

The comment about what is aggressive and what is not is complex.
Dive theories come and go. I can remember a period when extending dive time and getting out of the water quicker was all the rage. I can remember when a monitor II was the computer of choice for those of us doing deeper diving, especially when compared to the more modern computers of the time. Then we noted the bend rate on monitor II's, was significantly higher than the newer computers. Getting maximum time for minimum stops is not always a great idea. I have seen this cycle repeat with new 'theories' over the years. I like to know when I'm being a guinee pig, like when I started Trimix diving. I like to have some sort of handle on what risk I am taking.

If you are happier with the table, dive runtime. Though's of us that used to dive runtime, have adopted the new computers that are capable of nitrox, accelerated decompression, and mixed gas as they have become available.
Granted, I either carry two computers, or a backup runtime.

Gareth

[1] Sports Diver and above.

 

[Edward3c]

@Happy Spearo Welcome to the real world of diving.

You seem concerned about a minute or two of extra time at depth. It could be your’ve taken up the wrong activity.

I do many dives where I get nowhere near the line, and others where I will go past it and just do the mandatory deco (having first done the gas plan to ensure I'm carrying enough gas).

I plan the dive and dive the plan.

 

[Angelo Farina]

I think that the problem is your concept of "loosing time"...
We all explained that there are good reasons for employing a more conservative algorithm on a computer than the one used for calculating tables.
So diving with a computer is definitely safer.
And for most multilevel profiles, the computer requires less deco times and allows for shorter surface intervals.
For a truly square profile, instead, the computer forces you to slightly longer deco times. But remember, if the profile is truly square, the table is quite unsafe.
I used USN tables for 40 years, but always added some conservatorism with the following modifications:
1) ascent speed reduced from 18m/min to 10 m/min up to 15m, and then even slower at 5m/min
2) the diving time includes the ascent time up to the first deco stop
3) in case of cold water, anomalous effort or air consumption, or very square profile, step one row in the table (which usually means considering 5 minutes more).
All this said, I never "loose" time. I plan my dive and dive my plan. When I reach the 6m deco stop I look at my watch and depth meter, I look at the table and I evaluate how much deco is needed. Now instead I also look at the computer. And then I do the required deco. Where the hell can I loose time?
I can just end up making some more minutes of deco stop, which in general is not a problem, and in some case can even be pleasant (if you are on the reef).

 

[scubadada]

Hi @Happy Spearo

There is a problem here somewhere. The Atmos Mission One runs Buhlmann ZH-L16C, just like the Shearwater Teric and Perdix do. The owner's manual did not say what the GFs are for the 3 presets, so I emailed them. They replied that the presets are the same as those used by Shearwater. So, if you set your computer on Low conservatism, you should be diving a GF high of 95 and get an NDL of about 21 min. I don't know what the highest custom GF you can input, as stated, for Shearwater, it is 99. I would suggest making sure your computer is set to low conservatism and then go to the planner to check your NDL. You could also go to the custom setting and set a GF high of 95 (or higher if available) and recheck the NDLs. If you do not get the values you expect, you might want to contact Atmos or wherever you purchased the computer.

 

[Gareth J]

@Barnaby'sDad- I have that cert and understand that would extend my time. However, if my tables say I can stay longer then my computer on air at a certain depth, I am sure the tables are going to say I can stay longer with Nitrox at a certain depth then my computer on a Nitrox setting. Same problem with conservatism in the computer. I still lose out time and now I paid more for Nitrox. : )

You have answered your own question.

Ditch the computer, get a bottom timer, dive runtime.
Then you get the full time your table allows.

How that impacts on subsequent dives, or multi day diving I don't know. I don't know your tables.

I lose the more back to back dives I do if on tables. I am limited to 20 minutes of decompression time in any 24hours. I must take 24 hours off after 4 days. I cannot do more than 3 dives a day.
So, a trip to the Red Sea, I gain on the first dive, but lose over the week.
(Every one else is four to five dives a day, solid for 5 days.)

 

[johndiver999]

I always thought the USN gave 30 minutes at 90 feet?

http://people.uncw.edu/bullockw/index_files/ppts/tables_draft_1.0.pdf

 

[tursiops]

I always thought the USN gave 30 minutes at 90 feet?

http://people.uncw.edu/bullockw/index_files/ppts/tables_draft_1.0.pdf

Old tables.

 

[johndiver999]

Old tables.

so now they give more NDL time?

 

[tursiops]

Hi @Happy Spearo

There is a problem here somewhere. The Atmos Mission One runs Buhlmann ZH-L16C, just like the Shearwater Teric and Perdix do. The owner's manual did not say what the GFs are for the 3 presets, so I emailed them. They replied that the presets are the same as those used by Shearwater. So, if you set your computer on Low conservatism, you should be diving a GF high of 95 and get an NDL of about 21 min. I don't know what the highest custom GF you can input, as stated, for Shearwater, it is 99. I would suggest making sure your computer is set to low conservatism and then go to the planner to check your NDL. You could also go to the custom setting and set a GF high of 95 (or higher if available) and recheck the NDLs. If you do not get the values you expect, you might want to contact Atmos or wherever you purchased the computer.

View attachment 620006View attachment 620007

Good catch! If he has 17min NDL at 90 ft on air, then he is running GF-Hi of 85...i.e., the Medium setting on his computer.