Y JAEGER LECOULTRE, MASTER TOURBILLON, REF. 146.2.34.SAN 18 CARAT GOLD TOURBILLON WRIST WATCH WITH DATE AND DUAL TIME ZONE INDICATION, NO. 2397645, CIRCA 2007Movement: Cal. 978, automatic, 33 jewelsCase: 18 carat gold case, screwed down display case back with four screws, stamped with 18 carat gold common control marksDial: SilveredStrap: Jaeger LeCoultre black alligator strap with gold coloured double deployant clasp, stamped 750Size: 41mmSigned: Case, dial, movement, crown, strap, claspAccessories: Jaeger LeCoultre box, guarantee certificate, instruction book, loupe, outer card packagingThe tourbillon was invented by leading watch maker Abraham-Louis Breguet around 1795. It was designed to increase accuracy in a watch by placing the escapement and balance wheel in a rotating cage. This complicated mechanism is often exposed on modern watch dials, to showcase the skilled work. The Jaeger LeCoultre Master Tourbillon also features a date chapter ring on the outside of the dial. So that the date hand does not partially obscure the tourbillon, the hand will jump from the 15th (5 o'clock position) to the 16th (7 o'clock position), clearing the tourbillon.