The standard requires the ability to link pass a number of tests, including of course a battery of water resistance tests, and diver's watches must also possess certain design features, including the ability to be read in total darkness at a distance of 25 centimeters, and as well, they must possess a unidirectional timing bezel – this has been an essential feature of true diver's watches going all the way back to the early 1950s, when the Rolex Submariner and Blancpain Fifty Fathoms debuted.