Marv writes:

> how much weight will that suit require if we added 200cc of
> gas cells to it?  That is, it begins neutral at 15' with 16 lbs.

Well, if the 200cc were of water, it would weigh ~200g.

So if we simplistically assume that the gas is weightless and ignore the
3-4% density difference due to saltwater while we're at it, we would then
say that  200cc of gas @ 15ft would displace 200cc of water @ 15ft, and
thus, 200g.

With the ideal gas law (PV=nRT), we'd get the following rundown:

surface(1.0 ATM) - 300g
 15fsw (1.5 ATM) - 200g
 33fsw (2.0 ATM) - 150g
 66fsw (3.0 ATM) - 100g
 99fsw (4.0 ATM) -  75g
132fsw (5.0 ATM) -  60g
165fsw (6.0 ATM) -  50g