The part that covers the dial. It is generally made of glass and is fixed with a bezel. Its role is to protect the dial and hands from dust and shocks. For a long time, it was made of organic glass, but since the late 1930s, it has been made of glass that is less likely to break.Made of resinSince the late 70s, it has been replaced by thin and strongsapphire crystalSince the 90s, the technology to process sapphire crystal into a dome shape has been developed, which has contributed to the revival of classic designs.