Tissot ROCKWATCH, ca. 1985
Clever integrated Construction
Tissot has always been one of the brightest and most innovative children of the Swatch group. The movement is held in place by a plastic spacer first (grey in color). Then there is a steel cylinder with a circular groove for the O-ring. The case back with the integrated lugs is held in position by 6 screws. Yes I counted correctly, that 7th opening is not an opening, I simply left one of screws on the back of the case cylinder (left above the battery).
You can also see that the alignment of the watch is achieved by simple cut-outs for the lugs on either side of the case.