Sherwood Wisdom NDL question

[Pegger]

I know from the PADI tables that a dive to '100 ft, (just as an example), has a NDL of 20 min. I also know that the PADI tables are somewhat conservative for our safety as the navy tables have a NDL of 25 mins for '100 ft.
The Wisdom when you go into the plan mode has a NDL of 16 mins, and in the simulator mode asks you to go into a decompression stop after that 16 mins. Is this just another layer of protection?
The Wisdom uses a modified Haldanean algorithm.

Regards,
Steve

 

[Diver0001]

Yeah it just depends on the algorithm. Small variations like this are common and the best advice is to follow the NDL's your computer is showing you. The variations just go to show you that the NDL is an increasing grey-to-black area and not an exact line.

You may be able to find a setting on the wisdom to change the conservatism setting. I'm not familiar with that particular computer enough to tell you for sure but some computers have this feature.

R..

 

[DA Aquamaster]

I know from the PADI tables that a dive to '100 ft, (just as an example), has a NDL of 20 min. I also know that the PADI tables are somewhat conservative for our safety as the navy tables have a NDL of 25 mins for '100 ft.
The Wisdom when you go into the plan mode has a NDL of 16 mins, and in the simulator mode asks you to go into a decompression stop after that 16 mins. Is this just another layer of protection?
The Wisdom uses a modified Haldanean algorithm.

Regards,
Steve

This is pretty common for a computer. Tables make assumptions and set limits based on the idea that while it shows a square profile (diving to the depth and staying at that depth for the entire dive to the NDL), most divers do not actually do that, will round down to the next deepest depth (for example using 100 feet for a 91 ft dive), and may add some additional fudge factors such as next greater time or depth on a cold or working dive and next greater time and depth on a cold working dive.

In contrast, a computer dives a "square profile" all the time as it is constantly calculating depth and time and tracking nitrogen loading accordingly. The computer won't/can't fudge anything and any fudge would have to be with the diver watching the nitrogen loading bar graph and starting the ascent in the upper part of the green or in the lower to middle part of the yellow rather than bumping it all the way up to the red. Consequently the computer NDL's (and multilevel table NDLs as well for the same reason) are shorter.

In practice, on a 100' dive a diver will take a few minutes to get there and where the table assumes it's all at 100', the computer gives you credit for the shallower portions of the descent, so the actual difference on an actual square profile 100 ft dive pretty close to nothing with both computer and table divers starting their ascents at about the same time. And if any or all parts of the dive during that 16-20 minutes is actually shallower than 100', the computer credits that as well with the result that the computer will usually give you a longer bottom time without requiring decompression despite having a shorter NDL in planning mode.