The Omega Speedmaster Professional Moonwatch 310.30.42.50.01.002 is the current-generation Master Chronometer Moonwatch in the celebrated Sapphire Sandwich configuration, with sapphire crystals fitted to both the front and the caseback to reveal the redesigned Caliber 3861 chronograph movement that powers the modern Moonwatch lineage. The Speedmaster Professional Moonwatch traces its space heritage to 1965, when the model was flight-qualified by NASA for all manned space missions, and the 2021 fourth-generation refresh brought the Master Chronometer Caliber 3861 with METAS certification and antimagnetic resistance to 15,000 gauss into the same 42mm asymmetric steel Moonwatch case that has carried the model since the late 1960s. The 42mm stainless steel case is 13.18mm thick, with the polished sloping bezel carrying the engraved tachymeter scale, the twisted lugs, and the screw-down crown. The black step dial features applied luminous indices, the broad luminous baton hands, and the three black-on-black chronograph sub-counters in the classic Moonwatch layout. The chronograph layout places the 30-minute counter at 3, 12-hour counter at 6, and the running seconds at 9, with the central chronograph seconds hand. Pre-owned.