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.
Denuded skin is just another way of saying that the top layer (epidermis) of skin is gone...either from friction (abrasion or tear), trauma (tape burns), or severe rashes, or from a stage II pressure ulcer.
A gauge pressure occurs when the measured differential pressure is greater than the atmospheric pressure (), whereas a vacuum pressure is the opposite (). In both equations p is the system's absolute pressure and pa is the atmospheric pressure. See more Mechanical Engineering topics.