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Thread ID: 67493	2006-03-29 12:39:00	sea level pressure	Fergie (6508)	PC World Chat

Post ID	Timestamp	Content	User
441816	2006-03-30 22:28:00	Oooooooh! PINKY here in the US is the smallest finger on your hand...and thinking that way, Yes! I can see the reason for the paranoid thoughts! After all, the other fingers are all larger/stronger and more useful than it is........er...present company EXCEPTED! of course! Pinky is both a finger and a light shade of red here. I hope you get that Joe.	Cicero (40)
441817	2006-03-31 06:32:00	All the comments about sea level atmospheric pressure being variable around the globe makes me a bit nervous about the accuracy of dive tables. If the pressure is greater at sea level at a given dive site than the standard measure of 14.7lbs per square inch or its metric equivalent, then the dive tables will be out and a diver could unwittingly get into bends territory. Most divers are taught to treat dive tables conservatively and to allow a margin of error. And nowadays, I imagine that 99% of recreational divers going deeper than 10 metres use dive computers rather than dive tables, and I assume that dive computers compensate for variations like that through their actual pressure readings. However, in my dive training we were always taught that 1 atmosphere = 14.7 psi, and there was never any discussion about variations. I used to dive with a guy who would dive in the am and sky dive in the pm. Apart from the obvious question this raises about his sanity (!), this variability probably adds an extra risk for him (or anyone who flies in an unpressurised aircraft after diving).	John H (8)
441818	2006-03-31 06:49:00	:) You are worrying over nothing, but realise that the atmospheric pressure changes, not just aound the world but at the same spot :) However consider this, at 2000 feet altitude, the standard atmospheric pressure will have dropped from 14.7psia to about 13.7psia. But 1 psi = 27.7 inches of water gauge, and this is a very large change in atmospheric pressure. So are you going to worry about being about 1 or 2 feet out in your depth reading at the very most?	Terry Porritt (14)
441819	2006-03-31 07:49:00	There are separate tables for calculating diving times at altitude, so that isn't an issue Terry. In terms of your final point, I have a diving colleague who got the bends even though he stayed within table limits on two dives in a day. When the calculations were later re-done however, it was discovered that he went over the limits through snorkel diving between the two scuba dives. He was not subject to much more pressure, but it was enough to tip him over the edge, and bends was the result. The limits are quite precise; hence the need to treat the tables conservatively unless you want to end up impotent, incontinent, or dead. I have no idea whether the "1 or 2 feet out in your depth reading" could be significant, but I am not going to try to find out!	John H (8)
441820	2006-03-31 08:49:00	I mentioned altitude for 2 reasons, even though it may have seemed a red herring . 1) It takes 2000 feet of atmosphere to produce 1 psi . 2) Reduction in air atmospheric pressure is easier to produce by going up, than it is to increase pressure . The point I am making is that 1 psi (68 millibars) is an enormous change in atmospheric pressure at sea level . My domestic barometer reads up to a maximum of 1060 millibars, that is higher than the highest 'high' likely to be encountered in real life, so you will never experience a 1 psi pressure rise . But suppose atmospheric pressure increased by half that, 34 millibars from standard pressure, to about 1044 millibars, that is a very high pressure anti-cyclone, it would only increase the pressure on the sea, and hence your depth meter reading by 14" of water . I fail to appreciate that 14" depth variation is going to cause any alarm to any diver :) Edit: and that is why it was not mentioned in your diving training, it was not considered important!	Terry Porritt (14)
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