On Wed, Nov 21, 2018 at 6:43 AM Lutz Vieweg <l...@5t9.de> wrote: > > They are slow responding in air, but under water, it usually takes just a few > seconds > for them to change.
That's definitely not true. I looked at my dive profiles, and I see things like "it took five minutes for the temperature to stabilize". This obviously depends on the dive computer and some will be much better than others, but I really don't think the "temperature by depth" can work in general. You're much better off looking at the time progression, and just eye-balling how it matches with depth. For example, looking at my dives in Bonaire, there was a clear thermocline at around 105 ft on one dive, but almost all the other dives were pretty much "constant water temperature", so I can clearly look at just that dive. And I had four dive computers with me on that dive: - the Suunto EON Core tracks depth pretty closely, and with a delay of only about one minute. The profile looks sane and the temperature profile matches is well with a 0.1°C resolution, just delayed a bit. For nice slow descent/ascent, the one-minute delay is probably not even all that noticeable. - the Garmin Descent Mk1 only gives you 1°C resolution, but like the EON Core, it seems to be fairly quick to react (again, looking at the profile, I'd say "roughly one minute" delay). But the 1C resolution means that it's fairly noisy. - The Aqualung i770R gives 1°F resolution,m but the delay looks like it's about three minutes. - The Shearwater Perdix AI similarly gives 1°F resolution with a three-minute delay. The reason I say that the delay can be up to five minutes is that I look at the Shearwater profiles, and on the dives where water termperature was pretty much constant, it quite commonly takes about five minutes for the sensor to stabilize from the air temperature. Looking around at other dive trips: - Maui has almost no temperature gradients by recreational depths - Okinawa had temperature gradients, but the biggest ones seem to be only indirectly about depth. The shore dives show a big temperature gradient in shallow waters, but it looks like it's less about "shallow" and more about "close to shore". - some of my dives show temperature fluctuations that seem to have nothing to do with either surface or depth, and seem to be more about currents etc Basically, on the data I have, I don't really see anything that indicates that doing some depth-to-temperature mapping makes much sense. The thermoclines obviously *do* exist, but when they are clear they are quite visible from the existing time-based model, and most of the time they aren't clear at all and certainly not easy to associate with depth because of delays and other noise. Linus _______________________________________________ subsurface mailing list subsurface@subsurface-divelog.org http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface