Meet Jaeger-LeCoultre Master Ultra Thin (ref. 1378420), a contemporary classic shaped by careful watchmaking know-how. The exterior is thoughtfully executed: crafted in stainless steel and measuring 39 mm in diameter, with a thickness of 9.9 mm, defined by a round silhouette, paired with a gem-set bezel. The caseback is open, and the crystal is sapphire, delivering water resistance to 5000 meters. At a glance, the dial balances texture and clarity: a silver tone with sunburst finish, framed by stick / dot hour markers, and dauphine hands. At its heart beats a proven engine: the 938 caliber. With considered ergonomics, it feels composed during extended wear. Brushed and polished elements play with light to emphasize crisp geometry. For buyers researching specifications and real-world impressions, this reference stands out for coherent design, dependable mechanics, and lasting relevance within modern horology.