STS -99 Chronograph is a 42 mm round automatic chronograph designed and assembled in Towson, Maryland, using precision components manufactured in Pforzheim, Germany. This model continues the Mission Chronograph lineage, originally commissioned for NASA’s 2000 STS -99 Space Shuttle mission — the first mechanical chronograph worn in space in the 21st century. Its 316L stainless-steel case measures 42 mm in diameter, 13.5 mm thick and 20 mm between the lugs, combining a satin-finished mid-section with a polished bezel and exhibition back showing the movement. A domed sapphire crystal protects a silver dial with engine-turned registers, applied diamond markers and lumed hands, with a fixed tachymeter scale surrounding the dial for timing calculations. Inside is the Valjoux 7750 automatic chronograph movement, decorated and regulated by Towson watchmakers, offering chronograph and date functions and a 46-hour power reserve. Water resistance is 50 m. Each watch is numbered and delivered on a stitched leather strap with a stainless-steel deployment clasp. The STS -99 Chronograph’s provenance as a NASA-commissioned instrument and its transatlantic manufacture make it a significant piece for collectors of American-made tool watches.