This Patek Philippe 5101J is a landmark grand complication known simply as the 10-Day Tourbillon, and in yellow gold it represents the final expression of a reference that stands among the most accomplished watches Patek produced in the modern era. Its distinction lies in the pairing of two achievements: a concealed one-minute tourbillon and a remarkable ten-day power reserve, drawn from twin mainspring barrels at a time when most rivals offered only a few days of running. Powered by the hand-wound calibre TO 28-20 and chronometer-certified by COSC, it shows the hours and minutes, small seconds on the tourbillon at six o'clock, and the ten-day power-reserve indication at twelve. The yellow-gold case measures 51.7mm in height, 29.6mm in width, and 12.2mm in thickness, its stepped Art Deco form wearing with quiet elegance. A silver dial lends the watch a classical, understated character. A defining expression of Patek Philippe's technical ambition.