The "dog tooth ring" is called the outer ring of triangular pit, and Rolex is called oyster shell;
This outer ring was originally designed for screwing, fastening and waterproofing, but now it is a decoration. The outer ring of sports watch has the function corresponding to digital scale. The outer ring of the sports watch is used to measure the speed with the chronograph second hand, the diving watch is used to watch the diving time or measure the oxygen amount, and Greenwich is used to display the time in the second time zone. Explorers are used to observing day and night.