The pit does not have any magical properties. What turns the guac brown is the air. If you can keep air from touching the guac then it will stay green. The pit will keep a portion away from the air, but what is more affective is to put plastic wrap over it and push it right down onto the surface.
In my experience, denuded skin is when the top layer is off, sore is very superficial and usual caused from a shearing force. As above, there are many taypes of foam backed dressings used in teh VA, depending on which VA you are at. I am familiar Allevyn but here is a site where you can compare.
Absolute Pressure, Gage Pressure, and Vacuum. In a region such as outer space, which is virtually void of gases, the pressure is essentially zero. Such a condition can be approached very nearly in a laboratory when a vacuum pump is used to evacuate a bottle. The pressure in a vacuum is called absolute zero, and all pressures refernced with respect to this zero pressure are termed absolute pressures. Many pressure-measuring devices measure not absolute pressure but only difference in pressure.