Barometric pressure, a measure of the force of air, is frequently used in forecasting the weather. It is usually measured with a Fortin barometer, in which mercury is enclosed in glass, and travels up and down a metal tube in response to air pressure changes. A scale helps to match the mercury levels with the barometric pressure at the time a reading is taken. The Fortin barometer is generally used in meteorological stations as well as in laboratories and schools. In 2007, the primary manufacturer of the barometer discontinued production as mercury can be harmful to the skin and generally toxic to humans.