Rolex
First generation of "Swiss Made" dial with a flat 4 bezel insert. Circa late 1999. A series.
Throughout the production of the Sea Dweller 16600 three different lume materials and letterings at the bottom of the dial were used. The earliest having Tritium and marked SWISS T<25. In 1998 Rolex made the transition to Luminova and changed the dial lettering from SWISS T<25 to SWISS. In late 1999 they moved on to Super Luminova and changed the lettering to SWISS MADE.
Two bezel inserts were used, one having a flat 4 at the 40 mark which can be found up until the Y series in 2003. Rolex then switched over to the pointed 4.