I never said neutral at the end of the dive on the surface, I meant positive. It doesn't matter if it's slightly positive or really positive, the point is it's positive meaning that I won't sink unless I work at it.
That also means slightly positive at the surface at the beginning of the dive with a full tank (no air in wing). My theory is that my black or dark colored wetsuit has been out in the sun and the gas bubbles are pumped. That possibly supports the heaviness of the air I'm carrying, however even after a considerable surface swim sometimes where you'd think the suit would begin to cool off and the gas bubbles would get smaller I can still float, so who knows?
Then as I dive the suit obviously compresses and losses buoyancy at depth, this is where the need for a wing and a few huffs of air are needed. Then also at depth the ocean water begins to cool the suit so not only is it compressed but the gas bubbles are cooling and reducing in size also thus reducing buoyancy. So by the time the air is used up (5-6 lbs) I'm on my way up with a much less bouyant suit because suits don't just spring back to full size as you come up, it takes a while, and it's also cooled down. So the combination of the two has offset the loss of air weight somewhat to a trade off. This is how we are able to set our weighting so we can dive with no BC's. There's a lot more to it than just losing 5 lbs of gas.
The fine tuning of weight comes in play with every different suit I own and it's particular characteristics.
There's also the pure physics of the 15 foot stop, which is the most buoyant shift critical area in the water column as far as weight swing. This is why it's a stop BTW. And because of the wild weight swings at the 15' stop, I don't like to have any air in my wing because it sucks to have to constantly feather the trigger on the inflator and dump, so if I have to do that it obviously tells me I have too much weight on that doesn't need to be there. But I figured that one out on my own 15 years ago, with no help from any instructors BTW.
With my wetsuits: The cheap stuff smashes down something terrible, and my Rubatex suits spring right back, plus they are nitrogen filled so it's less prone to crushing. I took me a lot of diving and experimentation to figure all this out and I don't expect other people to take it to quite this degree, but it's what I do.
