This is an instrument for making precise barometric pressure correction in laboratory operations. It is also used in weather observations, factories, mines and power plants. The mercury cistern is constructed on the Fortin Principle adjustable to zero, indicated by an ivory point in the cistern. The glass barometer tube is carefully made and annealed and mounted in a brass metal casing. The Metrical and English system scales read from & from 640 to 810 mm with vernier reading to 1/100 inch and 1/10 mm. The mercury level is adjusted by means of a knurled screw mounted at the bottom of the casing. When the knurled screw is turned all the way into the casing mercury fills the entire system and the tube accepts a very small volume to allow for thermal expansion. The barometer tube and scales covering the glass are made from corning glass. The barometer is mounted on a polished wooden board fitted with metal thermometer. Supplied without mercury.