Is this true for dive computers?

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OK, it sounds like the statement in the US Navy Diving Manual does not apply to dive computers but relates to the mental shortcuts that metric users take in their calculations. IE: 10M = 1 ATM = 1 Bar, which is pretty close but not exact. I see nothing wrong with that for recreational divers estimating gas consumption or even decompression off tables but I found hard to believe that dive computers would be programmed that way.

Thanks all, I learned a bit. The Navy manual is not entirely incorrect but could be phrased more precisely given the almost universal prevalence of dive computers now. Example:

3. In the metric system, 10 MSW is defined as 1 BAR.

10MSW is not defined by the Metric system as 1 Bar, even the EU for dive computers. Divers using Metric tend to use it that way for rough calculations, computers don't. I think I will send an E-mail to NEDU.

It is interesting that Bars are no longer the proper (preferred?) Metric unit for pressure. I suspect it will be around a very long time for diving and weather since Pascals do convert evenly (by a factor of 10) to Bars but requires a lot more shifting of the decimal. The part that I always thought was strange is that one Bar is not an accurate conversion to the Standard Atmosphere, even though it was invented to measure atmospheric pressure -- IE the Millibar.
 
Back in the day we had some commercial diving done inside leaking wine tanks at around 14% alcohol...:)
I immediately pictured a Daffy Duck cartoon with him crawling out of a wine tank hammered!
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I immediately pictured a Daffy Duck cartoon with him crawling out of a wine tank hammered!
View attachment 440280

Back in the day we had some commercial diving done inside leaking wine tanks at around 14% alcohol...:)

The story I heard was the wine industry stopped hiring commercial divers because they lost less inventory by letting their tanks leak then allowing divers anywhere near them. :facepalm:
 
One of the requirements for getting an EN13319 approval on a dive computer, is the depth reading testing must comply with the EN13319 standards for a depth pressure. This is designed on 1020 kg/m³, which is typical of salt water in the temperate zones.
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No, 1020 kg/m^3 is quite atypical. It is an extreme surface value, corresponding to 35 g/l of salt (average ocean salinity) and 35 Deg C (very high surface temperature). Or, 30 g/l (very low salinty) and 23 deg C. Or, 28 g/l (even lower salinity) and 17 deg C (average ocean surface temperature). See Seawater Density Online Calculator.
 
10MSW is not defined by the Metric system as 1 Bar, even the EU for dive computers.
That would be a horrible definition, because 1msw depends on what kind of sea water.
It is interesting that Bars are no longer the proper (preferred?) Metric unit for pressure. I suspect it will be around a very long time for diving and weather since Pascals do convert evenly (by a factor of 10) to Bars but requires a lot more shifting of the decimal. The part that I always thought was strange is that one Bar is not an accurate conversion to the Standard Atmosphere, even though it was invented to measure atmospheric pressure -- IE the Millibar.
Yeah, bars are only tolerated by the purists. Again, since a Standard Atmosphere is just another definition, it is awkward to have one definition (bar) depend on another (atmosphere). The whole SI system is designed to get one back to fundamentals, not to derivatives of fundamentals. So, we use Pascals, which are 1 N/m^2, = 1 kg/m-s^2, which are all fundamental units. With the bar defined as 100,000 Pascal, we can get to fundamental units...with a lot of messy zeros. Note that oceanographers refer to depth in decibars (almost equal to a meter), since it is instrumentally measured with a pressure sensor. I have to snicker a little bit at the imperial-unit haters who insist their SPG be in bars, but do not stay consistent by talking about their depth in decibars. They really ought to refer to a 30db dive, not a 30m dive.
 
I can only speak directly for us (Atomic), but I'm quite sure that every dive computer is going to handle decompression calculations based only on actual pressure, not depth. ....
I agree with Ron.
We (DiveNav) do the same in our datalogger and our Smartphone Dive Computer
 
Yeah, bars are only tolerated by the purists. Again, since a Standard Atmosphere is just another definition, it is awkward to have one definition (bar) depend on another (atmosphere)...

"Measure it with a micrometer, mark it with a chalk, cut it with an axe."
--- "Foundation design", by Donald P. Coduto

I'm not so sure it is purists so much as those that work more from the engineering side of the process. A neighbor was a project manager for Boeing on some of their Mars landers projects. Pascals makes a lot more sense for his work.

For other readers:
  • 1 Bar = 100 kilopascals
  • 1 Standard Atmosphere = 760 mm (29.92 inches) of mercury (like in a manometer), 14.70 PSI, 1,013.25 × 10 3 dynes per square centimetre, 1,013.25 millibars, or 101.325 kilopascals
  • 1 Pascal = 1 Newton/M²
  • 1 Newton = force required to accelerate 1 Kg 1 Meter/Second/Second or 100,000 Dynes
Aren't all of you glad we cleared that up? :rolleyes:
 
"Measure it with a micrometer, mark it with a chalk, cut it with an axe."
--- "Foundation design", by Donald P. Coduto

I'm not so sure it is purists so much as those that work more from the engineering side of the process. A neighbor was a project manager for Boeing on some of their Mars landers projects. Pascals makes a lot more sense for his work.

For other readers:
  • 1 Bar = 100 kilopascals
  • 1 Standard Atmosphere = 760 mm (29.92 inches) of mercury (like in a manometer), 14.70 PSI, 1,013.25 × 10 3 dynes per square centimetre, 1,013.25 millibars, or 101.325 kilopascals
  • 1 Pascal = 1 Newton/M²
  • 1 Newton = force required to accelerate 1 Kg 1 Meter/Second/Second or 100,000 Dynes
Aren't all of you glad we cleared that up? :rolleyes:
LOL. I'm just glad I haven't had to use slugs since I was in mechanical engineering school.
 
There was a point back when, when USSR TV weather people started reading out conditions and forecasts in hecto-pascals. Every time was country-wide FTW moment.
 
And if you want to add a layer of confusion, try putting an atmospheric pressure reading into your dive computer as a means of checking sensor accuracy. You then need to explain to users who are not at sea level that most local weather sites one uses for reference don’t publish the actual atmospheric pressure, but a “sea level corrected” pressure, i.e. what the actual pressure would be if they were at sea level. That is unless the weather station is catering to aviation, when actual “station pressure” is used.

-Ron
 
https://www.shearwater.com/products/perdix-ai/

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