I've been wanting to pick up a vintage chrono (2 or 3 register). I see a lot of them on the 'bay from the 1970s that are diver chronos which have a diving bezel and relatively high water rating for a chromo (10 to 20 bar). Some brands are Tissot, Ardith, Croton, Waltham, Unichron, Lejour. All of them have either some 77xx valjoux or landeron, or lemania movement.
My question is how were old watches like manual winding chronos with no screw down crown/pushers, able to get such a high water rating?
It seems like todays chronographs barely even offer 50m water rating. Are those style divers watches par of a lost art?
Are there any modern diver chronographs that still have the proportions of the ones from the '70s? Like case sizes around 37-40mm with a manual movement, and 10bar+ WR?