At Baselworld 2015, ROLEX unveiled new-generation mechanical movement that sets a new standard of chronometric performance with criteria that surpass those of COSC (Swiss official chronometer testing institute)

The new-generation Day-Date and Lady-Datejust constitute a presidential couple at the cutting edge of Rolex’s technological innovation in terms of their chronometric performance. Equipped with the latest movements developed by Rolex – calibres 3255 and 2236 respectively – these models establish a new standard for superlative precision with criteria for precision on the wrist that are twice as exacting as those for a chronometer officially certified by COSC. Rolex has developed new high-technology methodology and equipment
to test the precision of its Superlative Chronometers according to the new tolerances, and under conditions that are more representative of those in which the watch is actually worn, simulating the wearer’s everyday experience. These exclusive chronometric tests complement the official COSC certification – to which all Rolex movements continue to be submitted systematically – and are carried out not on the movements alone, but on the assembled watches after the movements have been cased. As a result, the Rolex chronometers equipped with movements tested according to this new methodology demonstrate superlative precision on the wrist.