The SK utilizes the Orient in-house movement Cal. 469---one that Orient has been using since the 1970's---and is VERY reliable (I own 3 Orients with this movement). The other Diver appears to have the same movement---either way, the Cal. 469--is a 21 Jewel, 21,600 BPH, and a 40+ reserve.
The meaning of the numbers on the inner turning bezel 20M, 30 M, 35 M and 40 M in different colors had to do something with non-decompression times
The meaning of the markings are as follows: