Mass confusion about computers????

[tridacna]

Eric, you’re bringing up the rear of a revolution that’s already over. DCs have matured to the point where “blind trust” is no longer the deciding issue when deciding to use one. I dived tables for 30 years, changed to a DC 11 years ago and have never used a table again (Rec only). Get two cheap competing computers with similar algorithms if redundancy is also your issue. Cut a table and see if your computer is robbing you of precious BT. I guarantee on a multi-dive multi-day trip, your computer will be more accurate than any table you use. I’ve done 5 dives per day for 5 consecutive days and have never been dissapointed by what my SW or SP delivered in BT.

 

[BoltSnap]

Eric, you’re bringing up the rear of a revolution that’s already over. DCs have matured to the point where “blind trust” is no longer the deciding issue when deciding to use one. I dived tables for 30 years, changed to a DC 11 years ago and have never used a table again (Rec only). Get two cheap competing computers with similar algorithms if redundancy is also your issue. Cut a table and see if your computer is robbing you of precious BT. I guarantee on a multi-dive multi-day trip, your computer will be more accurate than any table you use. I’ve done 5 dives per day for 5 consecutive days and have never been dissapointed by what my SW or SP delivered in BT.

I bought my first dive computer few days before Christmas 1987 prior to my trip to the FL Keys. It was an AL/US Divers Datascan II (IIRC). It was AI and would give you your group Letter at the end of the dive. I upgraded it to the newer version a year later that was a "truer" multi-level computer but didn't give the group letter any more. I have NEVER used dive tables or looked back since then. The only time I use dive tables is when I am teaching scuba courses. I used dive computers from AL, Orca, Cochran, Suunto, etc. but now use Ratio with Suunto for personal use and Suunto, SP, AL in my dive school.

 

[scubadada]

...Honestly, I think you would be best served by a computer with a known, predictable algorithm. Even a liberal Oceanic has the potential to give you unexpected and unwanted results. Mainly meaning if you do happen to exceed your NDL, ever. Which, let's be realistic, with your experience diving Navy tables is a real possibility (not that I'm recommending it).

And that means (to me), get a Shearwater. It will never give you surprise penalties for anything.

Hi @stuartv

What kind of unexpected or unwanted results are you speaking of? Do you have real examples?

I've been diving DSAT for nearly 16 years, about 1450 dives. I've yet to be surprised by my computer's behavior. Nothing funny due to ascent, surface interval, dive profile... I frequently do 4, occassionally 5, dives per day. I often push NDL limits and about 5% of my dives have light deco. DSAT was not designed for deco diving. I don't know exactly how it handles deco, but it quickly adds time to the shallow stop. I've never had sufficient deco time to trigger a 20 ft stop.

I'm not at all sure the discussion about the various RGBM algorithms applies to DSAT (or PZ+), are you?

 

[tridacna]

Hi @stuartv

What kind of unexpected or unwanted results are you speaking of? Do you have real examples?

I've been diving DSAT for nearly 16 years, about 1450 dives. I've yet to be surprised by my computer's behavior. Nothing funny due to ascent, surface interval, dive profile... I frequently do 4, occassionally 5, dives per day. I often push NDL limits and about 5% of my dives have light deco. DSAT was not designed for deco diving. I don't know exactly how it handles deco, but it quickly adds time to the shallow stop. I've never had sufficient deco time to trigger a 20 ft stop.

I'm not at all sure the discussion about the various RGBM algorithms applies to DSAT (or PZ+), are you?

Craig, can you define”light deco”? Do you have a ceiling or not?

 

[Hoag]

I'm not trying to derail or hijack the thread here but this conversation has made me think of something that I had not thought of before.

One of the (perceived) advantages that people see in Oceanic computers, and one of the reasons I own two is that they offer dual algorithms. Do they not offer what amounts to 4 algorithms? They offer PZ+ and DSAT, but for each of those, they then offer an option to set Conservative: On or Off.

Doesn't this then give you 4 variations of which algorithm you select for you computer?

 

[Slamfire]

Garmin, Ratio, and Divesoft run Buhlmann with preset and/or custom GFs...

According to their literature, Ratio uses ZHL16B. Other Buhlmann GF computers use ZHL16C. C is more conservative than B. C was intended for implementation into personal dive computers.

 

[scubadada]

...So DSAT would be basically what the second gen PADI tables are based on, correct?

Exactly correct. The DSAT computer algorithm and the PADI RDP were released in 1987, based on the same data/analysis. From Deco for Divers, Mark Powell, "The M-values used for the RDP were adopted from the Doppler bubble testing and tested by Dr. Merrill Spencer and tested by Dr. Raymond E. Rogers, Dr. Michael R. Powell, and colleagues with Diving Science and Technology Corp. (DSAT), a corporate affiliate of PADI. The DSAT M-values were empirically verified with extensive hyperbaric chamber and in-water testing and Doppler monitoring."

 

[scubadada]

According to their literature, Ratio uses ZHL16B. Other Buhlmann GF computers use ZHL16C. C is more conservative than B. C was intended for implementation into personal dive computers.

Correct, I did not designate the version of Buhlmann used in these 3 brands. Buhlmann ZH-L16A proved insufficiently conservative in the middle compartments, B was modified for use in table calculations, C was further modified for use in computers. All 3 sets of M-values can be found in Deco for Divers, Mark Powell.

 

[tridacna]

. All 3 sets of M-values can be found in Deco for Divers, Mark Powell.

The big problem is that "Deco for divers" cannot be found. Unless you're prepared to pay megabucks.

 

[scubadada]

I'm not trying to derail or hijack the thread here but this conversation has made me think of something that I had not thought of before.

One of the (perceived) advantages that people see in Oceanic computers, and one of the reasons I own two is that they offer dual algorithms. Do they not offer what amounts to 4 algorithms? They offer PZ+ and DSAT, but for each of those, they then offer an option to set Conservative: On or Off.

Doesn't this then give you 4 variations of which algorithm you select for you computer?

2 algorithms, each with a native and a conservative version The conservatve version is run at the next higher altitude level compared to the native version. You can look these up in the NDL tables in the back of the manuals

Many computers have conservative adjustments for their native algorithm, that usually work by not fully specified mechanisms. Scubapro microbubble levels are one example.

Divesoft, Garmin, Ratio, Shearwater, all adjust conservativeness through preset and/or custom GFs for their native Buhlmann algorithms