HUB4700 The HUB4700 caliber is the successor to the famous El Primero caliber - the first chronograph with an integrated style automatic winding (1969), which was also the first mechanical chronograph equipped with a 5 Hz frequency (36’000 alt/h) allowing an accuracy of 1/10th of a second. In a perfect fusion between tradition and innovation, this entirely skeletonized movement is now equipped with silicon regulating element ensuring avant-garde performances, precision and reliability. Sapphire In search of the perfect fusion between movement and case, Hublot engineers and chemists have researched and developed a transparent material which reveals the heart of the watch, all while being robust enough to effectively protect the mechanism. That’s how the Manufacture has become the expert of synthetic sapphire, a material from which it derives its aesthetic qualities that are unique within watchmaking – transforming each watch into a work of art.