User manual inconsistencies: dive planner

Robert Helling helling at
Mon Aug 4 05:59:55 PDT 2014

On 04.08.2014, at 14:07, Willem Ferguson <willemferguson at> wrote:

> On 04/08/2014 13:20, Sergey Starosek wrote:
>> Willem,
>> Two questions regarding user manual:
>> In "Oxygen management" you use both 1.5 and 1.6 maximum allowed/deco pO2. Which one is correct? The default is ssrf is 1.6 bar.
>> You reference "mean depth" line in Planner but I don't see one. Was it copy/paste from profile description? Or did it disappear like axis guides?
>> Sergey
>> _______________________________________________
>> subsurface mailing list
>> subsurface at
> Sergey,
> 1. I THINK that this is what Robert communicated to me at some stage but I am not sure. We need input from Robert here, especially since some of the user manual for the planner was written before the finalisation of the planner UI. To be safe, I would keep all PO2max values in the user manual to 1.5, even if one can set it higher in the planner setup values. 

I don’t want to recommend anything. The planner switches to gases when they become available. That is determined as follows:

When you add a new cylinder/gas or change the O2 fraction of that gas, the planner calculates the “switch at” column to be the deepest integer multiple of 3m/10ft where that gas is allowed according to the deco pO2 setting. That can be overwritten manually by typing in that column.

The reason for choosing 1.6bar as default deco pO2 was that this gives MODs of 6m for pure Oxygen and 21m for EAN50. If you change to 1.5bar you get 3m/18m according to the above rule (which is not what I use and I thought 6m/21m are pretty much standard values). From what you can read, 1.6bar is a bit on the aggressive side but my impression is this is pretty much what everybody does with staged deco.

Therefore I would suggest to use 1.6bar as well for the examples of the manual since that does not lead to surprises for gas switch depth. But that is my subjective opinion.

> 2. This one is easy. Short reponse: The line for mean depth disappeared with the redesign of the planner UI, as did the axis guide lines. Long reponse: Maybe this needs re-negotiation for V4.3 especially since many dive computers report "Average depth" during and/or after a dive. As far as I am aware mean depth has no relevance to formal dive planning, but only for interpreting the dive plan after the fact.

Strictly speaking that is not the case. It can enter through the change of ascent velocity. Remember, some time ago, we had some discussion of how that was to be varied with depth. Unfortunately, many people do different things (some absolute depths like “last 6m always 1m/min”), some depending on the dive (“up to 80% of maxdepth”) or, as implemented percentage of average depth (which N.B. is the average depth — or arithmetic mean of depth if you prefer — of the manually entered part of the dive excluding deco as far as the planner is concerned). Catering for everybody’s system of rules would have lead to a UI nightmare so I decided to go with percentages of average depth as this allows to follow GUE’s rules as laid out on page 1 . After all, the ascent velocity does not influence the plan very much so I don’t think this is of much importance.


Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics
                      Scientific Coordinator
                      Ludwig Maximilians Universitaet Muenchen, Dept. Physik
                      Phone: +49 89 2180-4523  Theresienstr. 39, rm. B339

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