Hi.I was just reading an old post about packing, and part of it mentioned the use of a spirometer as a means to test the amount of extra air packing enables you to take in. Wouldn't it be possible (in a very basic, crude way) to use a simple balloon to get an idea of how much air you can take in? I know it wouldn't show the actual amount, but it could show how much more air can be inhaled one way or the other.