Experience the craft of Jaeger-LeCoultre in the Master Ultra Thin (ref. Q1378421), a distinctive model that balances proportion, precision, and presence. On the wrist, the case feels purposeful: crafted in stainless steel and measuring 39 mm in diameter, with a thickness of 8.95 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. Visually, the face is where character emerges: a silver tone with sunburst finish, framed by stick / dot hour markers, and dauphine hands. Mechanically, the watch prioritizes accuracy: the 938 caliber. The silhouette offers presence without excess, lending confidence in a range of situations. Finishing showcases disciplined attention to detail across facets, edges, and surfaces. For buyers researching specifications and real-world impressions, this reference stands out for coherent design, dependable mechanics, and lasting relevance within modern horology.