A Compression Case, often referred to as a Compressor Case, is a specialized type of watch case designed to enhance water resistance as external pressure increases. This mechanism utilizes the pressure exerted by water to compress the case back against the gasket, thereby improving the seal. As a diver descends deeper underwater, the increasing water pressure compresses the case back more tightly against the gasket, enhancing the watch's water resistance. This design was particularly innovative for dive watches, allowing them to maintain integrity and functionality at greater depths. The concept was pioneered by Ervin Piquerez S.A. (EPSA) in the late 1950s and became a hallmark of mid-20th-century dive watches. The Compressor Case is characterized by its spring-loaded case back, which is not fully compressed until subjected to external pressure, ensuring a secure seal only when necessary. This design not only provides practical benefits for divers but also adds a unique mechanical feature to the watch, distinguishing it from other water-resistant designs. The legacy of the Compressor Case continues to influence modern watchmaking, with many contemporary watches drawing inspiration from this classic design.