Transmitter pressures in the graph

[Magnus boden]

Hello,

I am in the process of migrating my dives from Shearwater into subsurface partly because of some nice feature and because I like opensource software.

I am trying to understand the logic behind the tank pressures in the graph.

This is a sidemount, stage and deco dive so 4 cylinders. I have transmitters on all cylinders except the oxygen.

For some reason it seems to hide whatever gas is set as initial gas so the part until my gas switch is not included.

If I add another imaginary cylinder and set it as initial gas then all transmitters are visible in the graph. This is not what I want to do but while troubleshooting I noticed this behavious. This graph is what I really would like it to always look like.

The logic which it seems to be is that it will only draw the gas your breathing currently only looks really wierd and ugly to me at least. I put in the actual gas switches between the sidemount cylinders just to see how the graph would look like.

It would be great if there was a configuration option to have it just draw all transmitters all the time.

What are your thoughts on this?

Best Regards

Magnus

[Michael Keller]

Hi Magnus.

On 31/01/26 09:02, Magnus boden wrote:

I am in the process of migrating my dives from Shearwater into subsurface partly because of some nice feature and because I like opensource software.

I am trying to understand the logic behind the tank pressures in the graph.

This is a sidemount, stage and deco dive so 4 cylinders. I have transmitters on all cylinders except the oxygen.

For some reason it seems to hide whatever gas is set as initial gas so the part until my gas switch is not included.

The problems one encounters when trying to make sense of dive logs of sidemount dives where tank transmitters were used have been discussed here in the past:

https://groups.google.com/g/subsurface-divelog/c/dSn-UzVZfig/m/20JE9eTzCAAJ

https://groups.google.com/g/subsurface-divelog/c/rZ89Ojc6tb4/m/NVhjptUaBQAJ

https://groups.google.com/g/subsurface-divelog/c/qGkPOhPhiWc/m/VmXWv8M5EAAJ

https://groups.google.com/g/subsurface-divelog/c/eFlgsbB4jx0/m/kxhOXHeaCAAJ

A recent change in Subsurface now allows the diver to re-assign the tank sensors to gas mixes in a clean way. But this still does not solve the problem that, for sidemount dives, essentially two tanks are used with the same gasmix, and no gas switches are logged when the diver switches between these tanks. Subsurface only allows 1:1 mappings between gasmixes and tank sensors (or 1:0 and 0:1) - not 1:2. And a lot of functionality in Subsurface is dependent on these mappings, like the calculation of SAC, or the functionality when merging dives, so there is no easy way to extend these mappings to allow 1:2.

If I add another imaginary cylinder and set it as initial gas then all transmitters are visible in the graph. This is not what I want to do but while troubleshooting I noticed this behavious. This graph is what I really would like it to always look like.

That's probably the easiest way to make your profile look correct. But note that the SAC calculation will be off, as the gas consumption of the additional tank is not considered.

Unfortunately it is also not easy for Subsurface to automatically add this tank, as there is no way to know which gasmix was the bottom gas without making guesses.

The logic which it seems to be is that it will only draw the gas your breathing currently only looks really wierd and ugly to me at least. I put in the actual gas switches between the sidemount cylinders just to see how the graph would look like.

This is the way to make the profile look and work correctly - SAC will be calculated correctly. But again, this cannot be created automatically as the dive computer does not log gas switches between the two bottom gas tanks in sidemount diving.

It would be great if there was a configuration option to have it just draw all transmitters all the time.

The way the logic in Subsurface works this would require us to make an assumption about what gasmix to use for this gas - I think it's preferable if we let the user select the correct gasmix for this tank.

Ngā mihi

  Michael Keller

[Magnus boden]

Hello,

Thanks for the answer, I would be happy with no change to the logic of sac calculations and only a visual change so the graph draw all the tank sensors at all times regardless of any gas changes. Is that also not possible without messing up the other logic?

Best Regards

Magnus

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