Rolex Gmt-Master : SCOC Dial vs. OCC Dial
OCC stands for Officially Certified Chronometer while SCOC stands for Superlative Chronometer Officially Certified. A seemingly insignificant wording on the dial will make a world of a difference to a seasoned and informed collector.
An OCC movement is one, which has successfully passed a test conducted by the Swiss Official Chronometer Testing Institute or COSC.
The test consists of testing a watch for 15 days and 15 nights putting it through five positions and 3 types of temperatures (normal, oven-heat, and refrigerator). OCC movements feature a regulator, which allow the wearer to manually adjust the movement to run faster or slower. The process of manually adjusting a movement can be cumbersome and inefficient.
The Rolex GMT-MASTER Ref. 6542 for example was fitted with an OCC movement while its successor the 1675 was not. These ones were fitted with SCOC movements.
A SCOC movement is an upgrade from the OCC. These movements have also passed the rigorous COSC testing but are not fitted with regulators, and this allows them to keep accurate timing for much longer.