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> what they do, and I was sick of talking about it on the net, I called them
and 
> asked.  They claim that the gauge measures depth in feet as = (ATA-1)*34.  
> That is, calibrated in fresh water at sea level. 

The U.S. Divers Monitor II did the same thing.  Chip Boyle and I 
disagreed how that translated to decompression profiles.  Chip thought it 
meant that the computer calculated the feet as you describe (i.e., ffw), 
and then used that feet value (rather than a representation of pressure) 
to plug in to the algorithm that calculates for deco (i.e., into a deco 
model for fsw), hence adding conservatism.  I thought it was just for 
calculating the number displayed to the diver, and that the deco model 
should have been based on pressure.  I guess if Chip is right, it does 
seem like a reasonable "fudge factor", because its magnitude increases 
with depth.

>  
> Note that capillary gauges, which many people use for shallow stops since
they 
> are accurate shallow, are "stupid" by our mutual definition, since they 
> measure depth = (ATA-X)*33 where X=ambient pressure at depth 0. 

That is a very good point, and not an obvious one, either.  On one hand I
think maybe people should be aware not to use such devices for altitude
diving.  On the other hand, it probably doesn't matter a hill o' beans in 
light of the other chaotic factors involved.

Aloha,
Rich

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