World Surveillance Group Inc (fka WSGI)

[trunkmonk]

pV = nRT (pressure * volume = the number of molecules * gas constant * temperature)
very predictable pressure-temperature relationship, very linear, no tricks and not hard to figure out because its the law and you dont have to do anything the balance the 2. when one changes the other changes, period.
atmospheric pressure, gravity(changes with altitude), and temperature figure into the bouyancy of an object, differntial pressure is what needs to be maintained.
helium has a boiling point of 4x that temp (-268), at -67 its well into gas state.
here is everything you need to know plus more:

http://www.omsi.edu/visit/physics/air/science/glossary.html#fluid