Dial, case and movement signed, in good conditionLATER BEZELDIAM: 39 mm THICKNESS: 13 mmNOTE: The first GMT model, reference 6542, was launched in 1954 and was immediately recognizable by the bright acrylic or bakelite bezel insert with the twenty-four hour markings printed to its underside. This material was chosen to reduce reflection which would disturb the pilots. The bezel ring was also made of acrylic and coated in an alloy to resemble metal. It then turned out that the flexibility of this material could cause the bezel insert to break and that in very warm environments the printing would often flake off. Consequently, Rolex decided to replace the acrylic insert against a more resistant metal version.