The Explorer II is equipped with calibre 3187, a self-winding mechanical movement entirely developed and manufactured by Rolex. In addition to the conventional hour, minute and seconds hands, it features a 24-hour hand to display a second time zone. The 3187 is fitted with a Parachrom hairspring and Paraflex shock absorbers, offering greater resistance to shocks and to extreme conditions. Like all Rolex Perpetual movements, the 3187 is a certified Swiss chronometer, a designation reserved for high-precision watches that have successfully passed the Swiss Official Chronometer Testing Institute (COSC) tests. Its architecture, in common with all Oyster watch movements, makes it singularly reliable.