Anyone who does a lot of diving has probably considered purchasing a water-resistant watch, and automatic diver watches are often the most coveted of all.

But how is it possible to take that nice piece of jewelry and subject it to the pressure of diving many feet under the water? And remember, the watch is not just sitting there in the water because even more pressure is being exerted as the diver moves through the water. How much pressure? Well at sea level you will experience 1 atmosphere of pressure, or ATM, and then as you move down every 33 free will be one more ATM.

So what keeps out the water? Well it’s a combination of the gaskets, or O-rings, and the seals that are formed at the “joints” where the crystal, the back of the watch, and the crown come in contact with the case.

The case and its thickness is also a factor in determining how water resistant a watch is.

The very best underwater watches will feature a case back and a crown which screw down. This provides a tight seal to keep out the water, with the back of the case forming a tight seal as a lid on a jar.

How far down into the water can you take these automatic diver watches? Well if it’s resistant to 30 meters, or 100 feet, not too far, maybe the sink and that’s about it. Water resistance to 100 meters, or 330 feet is fine if you want to do a little snorkeling. However, if you have a diver watch rated for 200 meters, or 660 feet, you can get your scuba gear ready.

Remember also when considering your new dive watch, go for overkill rather than a conservative choice. In other words, buy a watch that’s rated for more depth than you need. Better safe than sorry.