Subsurface deco calculations

Rick Walsh rickmwalsh at
Fri Feb 3 22:27:00 PST 2017

On 4 February 2017 at 15:53, Miika Turkia <miika at> wrote:

> Hello,
> I cannot currently log into my gmail account due to 2-factor
> authentication challenges (cannot receive SMS at the moment), so using
> my private email, with hopefully correct addresses see-and-pasted from
> my phone :D
> Anyway, the attached log calculates quite different tissue saturations
> for different DCs, the worst being with OSTC Sport with shallowest
> depths by the sensor.

I hope you had a nice dive with the threshers.  If you can have a beer at
the Craic House (Evolution) and tell Dannie I say hi.

I can see why the OSTC Sport is giving greater tissue saturation and deco,
and it has nothing to do with how the deco calculations are performed.  The
problem is that the xml references a cylinder with index 1, but you only
have one cylinder defined (index 0), so it looks (without checking the
code) like Subsurface is assuming any undefined cylinder contains air.

The xml entry for the Suunto Vyper Air specifies a change to cylinder 0
(which is EAN32) at the start of the dive on lines 22 and 23:
  <event time='0:00 min' type='25' flags='1' name='gaschange' cylinder='0'
o2='32.0%' />
  <event time='0:00 min' type='25' value='32' name='gaschange' cylinder='0'
o2='32.0%' />

The xml entry for the OSTC specifies a change to cylinder 1 on lines 158
and 159
  <event time='0:02 min' type='25' flags='2' name='gaschange' cylinder='1'
  <event time='0:02 min' type='25' value='32' name='gaschange' cylinder='1'

The Suunto Stinger log does not specify a gas change at all, so the default
is the only defined cylinder, which contains EAN32.

Could I guess you had at least two gasses defined in the OSTC that were
downloaded, the second (index 1) of which was EAN32?  You could have then
merged the dives and deleted the unused gas/ses, but the OSTC profile was
still referencing cylinder 1.

Maybe the default assumed value for an unknown cylinder would be cylinder
0, and if no cylinders are defined, THEN default to air.

> I have set GF 30/75, if that matters.
> Any idea if this should somehow be expected or bug somewhere?
> miika


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