Barograph Recording Instrument - Brass & MahoganyMechanical barographs have a solid rotating brass drum that is driven by a quartz battery movement to rotate the drum once a week. A felt tip pen at the end of the of the writing arm shows changes in the air pressure on a paper diagram that is wrapped around the drum. A mechanical barometer movement with four round diaphragms measures variation in the air pressure and transfers it very precisely through a system of mechanical levers to the writing arm. All barographs come with a supply of charts and felt tip pens for one year.Specifications:Housing: 195 x 125 x 127mmWeight:1,310g