The Rolex Explorer was created as a larger sibling to the Explorer I and designed with spelunkers in mind. With its 24-hour bezel markings and 24-hour hand, spelunkers, who would often be exploring caves in the dark and unable to differentiate between morning and night, would be able to tell whether they were looking at am or pm by the position of the 24-hour hand to the bezel. The Ref 16570 was produced between 1989 through 2011.