Casio Men's G-Shock Master of G Series Gravitymaster GR-B300-1A4JFProduct Highlights The GR B300 GRAVITYMASTER features a shock resistant structure called the "Carbon Core Guard Structure," utilizing the characteristics of carbon material used in aircraft bodies (impact resistance, rigidity, and durability). By combining a case made of carbon fiber reinforced resin with a seamless bezel inspired by next generation aircraft, it achieves a powerful form as a GRAVITYMASTER. Designed with features like a Flight Log