Has any brand ever made a watch with a completely vacuum sealed case? I don't know if sapphire crystals are strong enough to support a vacuum, but if they are it seems like it wouldn't be hard to do and it might reduce air friction on the balance weel. That friction is probably negligible but I...

I'm curious, what does water resistance REALLY mean? I have a Tissot PRS516 Automatic which says "50 meters". I'm assuming this means I can go under water to a depth of no more than 50 meters. Does this also mean that I can wear my Tissot in the shower? In a Sauna? I also had the watch...