Thanks Smidsy. Science appreciates you.
OK, lets translate that into English for people who want to know what the hell this all means (like me):
Check my numbers, but I'm trying to translate the pressure test into what I can really do.
I have an Invicta that claims to be water resistant to 100 meters/330 feet, but those in the know (including the instructions that came with the watch) say that means you can wash your hands and swim with it, but really only swim if it has a screw down crown.
From wikipedia: 14.7 psi=1 ATM. That's the air pressure we face at sea level.
When In water: for each 10 feet of depth, figure about 4.4 psi increase in pressure.
So to use round numbers: 30 psi is ~2 ATM, 45 psi is ~3 ATM
Going 10 feet deep in a pool is about 44 psi. I used those numbers to create this table:
Depth...........PSI...........ATM
0................. 14.7..........1.0
5 .................36.7..........2.5
10................58.7..........4.0
330..............1489.........101.0
(Whew. It is
impossible to make tables in these posts)
Conclusions:
1) Use of the term ATM to describe what a watch can tolerate is TOTALLY useless. Nobody dives in a 4 ATM pool, they dive into a 10 ft pool.
2) My watch can handle 300 feet? NFW. I'd be at 101 ATM. It would fail, and so would I.
3) The numbers on the watches are BS (but we all knew that)
4) To feel that a watch is "safe" to wear when diving in the average 10 foot deep pool, it should be able to be subjected to a preesure test at 58 psi without showing a real rapid stream of bubbles when the pressure is dropped to indicate that it's water resistant at that level (Rolex calls their watches 'pressure resistant')
Sound correct?
References:
wikipedia.com
http://wiki.answers.com/Q/How_much_does_water_pressure_increase_per_vertical_foot
