First, the movement alone is submitted to the testing criteria governing the ‘chronometer’ designation for wristwatches.

A rate deviation of between –4 and +6 seconds per day is tolerated during these tests. After casing the movement, the precision of the finished watch is then tested according to a protocol developed by Rolex that simulates actual conditions ʻin wear’. The rate deviation tolerated by the brand is much smaller: –2/+2 seconds per day.