kanerich Posted May 27, 2006 Report Share Posted May 27, 2006 in salt water. atm = depth in ft/ 33 i.e. 4atm ~ 132ft. It doesn't really matter salt water or delicious jello pudding. Atm is a metric measurement, and as such it is not mathematically defined in feet, although it is done so in England and the US out of convenience, not accuracy. Your formula is a rule of thumb, not an actual formula. Quote Link to comment Share on other sites More sharing options...
offshore Posted May 27, 2006 Report Share Posted May 27, 2006 It doesn't really matter salt water or delicious jello pudding. Atm is a metric measurement, and as such it is not mathematically defined in feet, although it is done so in England and the US out of convenience, not accuracy. Your formula is a rule of thumb, not an actual formula. Yes... someone who knows their stuff And we can argue, if needed, that 132' can also equate to 5atm ( absolute)- you need to add the atmosphere we are always surrounded by, ie. air pressure. ( 14.7 psi @ sea level)...... accepting of course that an atm doesn't actually equal any depth as stated above! Pedantic- probably, but nevertheless very relevent to the diving fraternity!! Try planning a deco stop, for a dive in freshwater ( marginal change in pressure and therefore calculated depth), in a cave or lake which is at altitude. There's not a deco meter available- even today, which can account for all these variables. So break out the tables my lads, and argue whether US Navy tables, or British are the more conservative. One case of the bends, and ongoing problems with bone necrosis finished my diving days, so I can factually tell you what tables I would dive to! Offshore CMAS ***** Instructor-1976 Quote Link to comment Share on other sites More sharing options...
Edge Posted May 27, 2006 Report Share Posted May 27, 2006 Offshore is 100% spot on and so are the others who mentioned that Atm are non attributable directly to depth. ATM is a measurement of pressure not depth and pressure is dependant upon the medium and other environmental factors, such as altitude, and global position (lat/lon). All of these factors and more contribute to the pressures felt and therefor NO device or table is ever 100% accurate, hence the fact that US and UK and other diving tables give a conservative estimate based on the law of averages and statistical possibilities, they are not factual but merely a guide, as to the best estimates availabe and also conservative to try and be as safe as possible. Edge! Chemist/Physicist Quote Link to comment Share on other sites More sharing options...
lagae Posted May 27, 2006 Report Share Posted May 27, 2006 All I wanted to know was if I had to take off my PAM when it rained or when I had to get something out of the sink or bath with both hands. Now I know it's safe to shower in. I'm not a swimmer really, and I don't wrestle crocs or fish or play about on boats, so for me, the 3" test is fine. Be careful about the shower. Getting rained on or taking something out of the sink is fine, but I'm not sure how good that test would be for shower use. It's possible you could have a very hard spray of water coming from the shower, and the warm temperatures may also adversely affect the water resistance. Personally I don't worry about my watches after I've tested them and often get them wet, but I still don't wear them in the shower or in a hot tub. Quote Link to comment Share on other sites More sharing options...
Pugwash Posted May 27, 2006 Author Report Share Posted May 27, 2006 and the warm temperatures may also adversely affect the water resistance. This test used very hot water ... it heats up the watch, expanding the air inside, adding a fraction of a second of safety barrier in which you can whip out the watch before water gets in. That's the theory, at least. It does mean that the test covers hot water as well. Quote Link to comment Share on other sites More sharing options...
_jonte Posted October 11, 2010 Report Share Posted October 11, 2010 Sorry for reviving such an old thread, but I thought I would give some input to this suggested MacGyver testing method. I would say that the method (theory) does not work, and don't try it! Why?... Well simply because heat transfer is not instant "enough". (moment of inertia, kind of...) It would take a few seconds until the heat reaches the inside of the watch enough and to heat the air to expand. Within these few seconds water will have the chance to slip inside. In other words, pressure build-up is not instant. Also, if anything, the thermal expansion of the watch should start sooner than heating of the air inside, thus lowering the pressure inside. Of course this would effect would be marginal. I don't have the wish to do the math on this, but I'm fairly sure my theory applies. My only proof though is general "engineer reasoning". What are your thoughts? Quote Link to comment Share on other sites More sharing options...
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