Forskellen på to seiko modeller ?

[hannover_dk]

I understand completely the thing about gaskets which can withstand helium from coming into the watch - which is of course for Helium chambers - and if helium can penetrate the watch, then once the diver is out in free open air, the crystal can pop of due to the higher pressure inside the watch - from helium which may have penetrated under higher pressure, and now escapes by puffing of the crystal.

Here several watches Seiko/Iwc - (and the old ploprof I THINK) do not have a helium valve, but is constructed much stronger - especially with regard to the crystal-fitting, and they are safe with helium tanks still.

What I do not understand is the bit about the rating for depth, where some watches can "withstand mixed gas" used for saturation diving - as I believe that to be the mixed gas in bottle (and not air or oxygen as for shorter dives) as the watch can never get in contact with that mixed gas

It is also hard to understand that those watches which can withstand mixed gas used for saturated dives can also withstand diving in over 200 meters depth for a longer period? I would have thought if it could withstand the pressure in 10 minutes, then it also could do that for 35 minutes, but there I may be wrong.

The fact that for saturation diving, the diver is down much longer time, is correct and also that the diver also requires helium tanks for the return. For that the special gaskets withstanding helium make a lot of sense.

I think I am probably just missing the clue, and hopefully - one day - I well find it (if not I will live happily)
br