Rolex watches are mostly all rated to run wthin COSC, depending on age. But there is no single rating for "every" submariner--yours might be + 1 second and mine might be + 4 seconds, but within -4 to + 6 seconds per day range. The Submariner shares the same movement with several other Rolexes and has been many times commented on as being robust, reliable, and accurate. If you have one running outside the specs, assuming it is reasonable new (within 10 years or so) you can send it to your dealer or Rolex for adjustment. If you are thinking of buying, Rolex as an automatic watch company manufactures some good movements and most people report good results.