ok. being new to watches in general I've got to ask.
what makes a dive watch a ''dive watch''?
Dive watches typically represent the best a manufacturer can do in water resistance, shock resistance, general ruggedness and luminescence. They appeal to non-divers who want a rugged tool watch. Of course divers wear them too, even today, although they have been eclipsed by dive computers.
This is the Seiko dive watch I'm wearing today:
I need to repaint some of the bezel numbers with acrylic enamel and a fine brush.
The first water resistant watch was the Rolex Oyster (1926). Mercedes Gleitze wore one for her English Channel swim on 21 October 1927. The first diver watch was the Omega Marine (1932), an industrial watch, followed by the improved Omega Marine Standard (1936) which was sold to the general public. The first modern diver watches were the Blancpain Fifty Fathoms and the Rolex Submariner (1953). They had all the features we expect in this sort of watch today and there are innumerable copies.
No watch is water proof. An entry level diver watch has 20 ATM (atmospheres) water resistance. A manufacturer like Seiko pulls one every X number of watches off the assembly line and sends it to quality control, where it is placed in a water vessel and pressurized to 20 atmospheres to see if any water gets in. Watches like this may be used for sport and military diving to a depth of 100 feet, or even a few feet deeper if you're feeling lucky. In commercial advertising, you will see 20 ATM translated into 20 "bars" (which they think is your general orientation) or even "200 Meters." Guys, no one dives to 200 meters. That's what submarines are for.
Diving 10 to 30 feet underwater, you will see all the marine life and scenery you could want to see, and the biggest pirate treasure ever found was 10 feet underwater off Long Island. If you go deeper, it gets cold and dark really fast. If you dive to 90 or 100 feet, to see a wreck I guess or just to say you've been there, you'll need to bring your own light and grease yourself to pull on a dry suit.
There are people who dive below 100 feet because it is their job, and they wear professional diver watches with WR from 150 ATM up to ridiculous numbers and certification for outer space! Not going there.