The Seiko Prospex Baby Tuna SRP639K1 is a great watch for diving and water sports. It's designed for people who love the ocean and need a reliable timepiece. With a 200m water resistance, it can handle deep dives. It has a black dial, a rubber strap, and a stainless - steel case. The approximate case diameter is 48mm and the approximate thickness is 13.8mm, making it a substantial yet comfortable watch to wear.