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> This is NOT true for at least some computers and digital gauges (e.g., the 
> Aladin Pro, and maybe also on the Uwatec digital depth gauge I normally use).

> My understanding is that these sense the decrease in atmospheric pressure at 
> altitude and compensate for it, effectively resetting the pressure for depth
= 
> 0 from 1 Bar to < 1 Bar.  This means that the absolute pressure at an 
> indicated depth of 20 ffw is less than that at sea level.  


Are you sure about that?  It seems to me that these computers should be 
taking a pre-dive ambient pressure reading so that they know what 
pressure to decompress the diver "to".  I can't imagine they adjust the 
numbers that they read on the depth scale (= the numbers that they 
indicate as decompression ceilings) just to give the diver a better idea 
of the linear feet bewteen him.herself and the surface.  Maybe they do - 
the only advantage would be that the computer wouldn't read "0" at 4 feet 
(or whatever 1 bar would be).  But my understanding is that, because many 
divers use analog gauges, and therefore follow decompression stops 
according to ambient pressrues as it would be in saltwater at sea level, 
it would be dangerous for a computer to depart from that standard.  
Personally, I think we should all measure our depth in terms of atm or 
bar, rather feet or meters, because all of the physiological stuff is 
keyed to pressure, not linear feet from surface.

Sorry is I added to any confusion.

Aloha,
Rich

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