Brass-cased model 5800 'Atmos Classic' clock, serial number 437226. Jaeger-Le Coultre's famous 'Atmos' clock was first developed in 1928 by Neuchâtel engineer Jean-Léon Reutter and introduced into Jaeger-Le Coultre's product range in the early 1930s.

It is a torsional (twisting) pendulum clock with ‘detached lever’ dead-beat escapement. The clock is automatically wound without any intervention by the owner. Changes in air temperature and pressure cause a liquid- and vapour-filled chamber at the back of the movement to expand and contract, winding the clock's mainspring. A change in temperature of 1° can provide enough power to run the clock for two days, and the mainspring has enough power in reserve to run the clock for a year.

Energy is conserved by the very slow-moving twisting pendulum which 'beats' only twice per minute. The movement is so slow and the parts so finely finished that no oil is needed.

Atmos clocks are frequently given as official gifts by the Swiss Government to famous and important visitors, including John F. Kennedy, Winston Churchill, Charles de Gaulle, Charlie Chaplin and Pope John-Paul II.