Tudor Black Bay 58 GMT Watch, 39mm Black Dial, M7939G1A0NRU-0002The Black Bay GMT is an extension of the Black Bay line with a highly functional complication: a multiple time zone function also known as a GMT function. Recognizable by its rotatable bezel, which derives its deep blue and burgundy colour theme from other models in the Black Bay line, but in a matt version, the Black Bay GMT is also a nod to the early days of this watchmaking function.