The Professor's Barometer was an invention created by the Professor used to read local atmospheric weather conditions around the island. Utilizing a memory disc that fell to Earth from the deteriorating Russian Seti Satellite, it appears to have worked as an aneroid barometer, utilizing air pressure on a metal cell of indeterminate structure expanding and contracting from air pressure. Decreasing barometric pressure indicates storms, rain and windy weather. Rising barometric pressure indicates good, dry, and colder weather. Slow, regular and moderate falls in pressure suggest a low pressure area is passing in a nearby region. Marked changes in the weather where you are located are unlikely. Small rapid decreases in pressure indicate a nearby change in weather. They are usually followed by brief spells of wind and showers. A quick drop in pressure over a short time indicates a storm is likely in 5 to 6 hours, and large, slow and sustained decreasing pressure forecasted a long period of poor weather. The weather would be more pronounced if the pressure started rising before it began to drop. The Professor used the disc to read indications of a tsunami similar to the one that brought Duke Williams to the island, but one of greater volume and tendency to wash the Castaways off the island to their rescue. Gilligan kept the disc after the return to civilization as a good luck charm until it was taken as evidence by the FBI.