Be careful doing heavy packing!! Just saying.
The easiest way is to inspire at maximum with packing, and exhale completely into a large ballon.Then, inhale the air from balloon, so what remains is packed air,the amount can be measured.
Wow, that is simple and brilliant
Just to make simple things complicated
there's probably a slight difference between the amount of air estimated from buoyancy change, and the amount of air packed, since TLC is under slight pressure after packing. I don't know how much at all, probably not a lot as far as I remember from an old thread. However see below.
What is the purpose of estimating it? Air volume in litres?
7,5 lbs - 5 lbs = 2,5 lbs buoyancy change = 1,13 kg wich is equal to 1,13 litre. This is at surface level. Very similar indeed to Bills experience.
At a 2 meter depth measure point (bottom of pool) the difference might equal a slightly bigger volume taken down as far as I can tell, equal to around 0,23 litre change, since both airspaces are slightly compressed, and the difference will the be a little bit smaller: At 2 m air will compress to app. 83 percent. Reversed it show a 1/o,83=1,2 = 20% volume increase taken up to surface... A TLC around 7L, and a TLC-pack at 8,13L (equal 2,5 lbs change) measured at 2 m, would then equal 1,2x7 - 1,2x8,13 = 1,36L (or easier 1,13 x 1,2 = 1,36). So that's a 1,36-1,13 = 0,23 L addition to the calculation trying to adjust for pressure-biased measuring. Still added is totally 1,36 L of packing at surface.
Then you have a factor of packing compression to calculations, say mayby 5 % increase of TLC+pack lung pressure when packing (just a wild guess) at surface: (TLC+pack) x 0,05 = fx 8L x 0,05 = 0,4L that doesn't show in buoyancy change at surface: You got more air, but it doesn't take up more space, it is just under pressure. At 2 m it would suddenly show itself in buoyancy change again I guess, so you can't combine the factors.
On a side note: I just realised that pressure change in lungs does not "start" at packing level, it is something that increases gradually at any inhale above passive-exhale-level. Now this might not make a big difference to the above calculations, but I just realized that "packing" is really something you do with your mouth - a technique - not something that describes a "point of pressure change" in lungs, since they are allready being gradually forced to hold more air/pressure. Full inhale is just the point where your muscles can't force more air in on any given day...
Disclaimer: Not sure calculations are correct, but this is what I came up with
