Question deco stop display differences between subsurface and shearwater app

[Mario007]

anyone know how to set up either software so the deco stop will matched between the two software ? as far as i can see the setting are the same but perhaps i missing something

 

[L13]

Shearwater is displaying the required deco stop depth. Subsurface is displaying the instantaneous ceiling(rounded to 3m/10ft). They are different things.

 

[harvalen]

Apart from the required deco stop and instantaneous ceiling being different things, there are also rounding errors and choices in the implementation of the algorithm that results in small differences.

Why is Bühlmann not like Bühlmann – The Theoretical Diver

thetheoreticaldiver.org

You should be able to show the Shearwater deco stops in Subsurface by clicking the "Toggle DC reported ceiling" button to the left of the graph.

 

[Nomader]

Hi,

I'm finding the same thing. Is this another example of the difference between instantaneous and required deco stops? The red is the Shearwater stop and green is Subsurface calculation.

 

[stepfen]

Hi,

I'm finding the same thing. Is this another example of the difference between instantaneous and required deco stops? The red is the Shearwater stop and green is Subsurface calculation.

Except from the rounding differences discussed above, it seems that the final stop depth is different. Subsurface uses 3m (I think that this is fixed - user can't change it), while your DC is set for 6m (user can change this from the settings).

 

[Nomader]

Except from the rounding differences discussed above, it seems that the final stop depth is different. Subsurface uses 3m (I think that this is fixed - user can't change it), while your DC is set for 6m (user can change this from the settings).

Yes. I’ve changed the final stop depth to 6m. Good to hear the rest of the differences are explained by rounding etc.

 

[L13]

Except from the rounding differences discussed above, it seems that the final stop depth is different. Subsurface uses 3m (I think that this is fixed - user can't change it), while your DC is set for 6m (user can change this from the settings).

SubSurface can be set for last stop 6m/3m (20ft/10ft).

 

[stepfen]

SubSurface can be set for last stop 6m/3m (20ft/10ft).

How? Nothing relevant in the preferences.
All I can see, is in the planning mode. Nothing for imported dives.

 

[L13]

How? Nothing relevant in the preferences.
All I can see, is in the planning mode. Nothing for imported dives.

For recorded dives, the depth you stopped is the depth you stopped. Not sure what you are asking for. The ceilings can be displayed either as continuous curves, or quantized to 3m/10ft. Is that what you are referring to?

 

[harvalen]

All I can see, is in the planning mode. Nothing for imported dives.

The ceilings can be displayed either as continuous curves, or quantized to 3m/10ft.

That's an important distinction. The green ceiling is just the calculated ceiling, not the planned deco stop. It won't take things like off-gasing during ascent into account. In the planner you see the deco stop in the dive profile and dive plan details. For a recorded dive, the calculated deco stop and tts will only be shown in information overlay for the specific point you hover over with the mouse pointer. It won't take things like last stop at 6 m into account, but in the end the depth where you did your stop is the depth where you did your stop.

In both the profiles above we have a deepest ceiling that's 3 m deeper than the first stop by the Shearwater. It could be a mismatch in GFlow, but likely it's just that the fast tissues are expected to off-gas enough during ascent so the first stop starts 3 m shallower.