The helium escape valve was specially developed for use by professional divers. During deep sea dives lasting several days, divers operate from diving bells. Prior to surfacing, these bells are filled with a mixture of helium and oxygen. The helium molecules are lighter than air and can therefore penetrate the watch in sufficient quantity to push out the crystal at atmospheric pressure levels. This can be avoided by opening the valve during resurfacing, which allows the helium to escape, while preventing water from entering the watch. Please keep the helium valve closed when the watch is in contact with water.