Mechanical 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 writing arm shows changes in the air pressure on a paper diagram that is wrapped around the drum. A mechanical barometer movement with eight round diaphr agms (four in the case of the model 2018) measures variation in the air pressure and transfers it very precisely through a system of mechanical levers to the writing arm. The models 2001, 2004 and 2006 have additional oil damping of the arm to avoid incorrect readings when on ships and yachts. The high-quality mahogany case is polished several times and treated with a special high-gloss lacquer for the models 2003 and 2004 to produce an especially lustr ous surface. The interior metal parts of these two models are solid brass, polished and gold-plated. The case of the model 2018.2 is black piano high-gloss finish, the baseplate is of brushed and nickel-plated brass, and the metal parts are chromed. All barographs come with a supply of charts and felt tip pens for one year.