[ejunge]

So what kind of forces can a swimmer/diver apply to his/hers watch? first we have the depth ofcourse. If we use a watch similar in size to a Raysman. Lets say we are at 100 meter depth. The size of the watch is about 5cmX5cm thats 25cm2 in surface area. 1m is 100 cm so 100m is 10.000cm 10.000X25= 250.000 Cm2 of water above the watch that is pressuring against it. The weight of that water is 1000.000/250.000= 250Kg(550 ibs) of pressure against the watch at that deptht. This is known as the hydrostatic pressure.

The diver(staying at the same depth) can only change that pressure against his watch in 2 ways either by moving his arms up or down but the maximum reach of ones arms is very limited usually not more then perhaps 120cm(4') or so.... that is only a change in pressure of 0.12 bars or 3Kg(6.7ibs) of pressure, very little difference not much more then 1% compared to the rest of the pressure at that given depth.

Second way to increase pressure at the watch is trough speed/acceleration. Either by swimming or by moving our arms up and down. The maximum speed we can move our arms in free air is often not more then 3-6 feet per second and it moves even slower under water. And when it comes to Swim speed even an Olympic swimmer usually cant swim any faster then 6-7 feet per second. If we add the maximum output of that we get up to 10 feet or 3 meters of acceleration per second which is the equvivalant of about 10Km/h or 6.25 mph. That aint very much force/pressure in water. Someone smart here at the forum(CycloneFever) calculated this and I quote:

"Without repeating all the calculations here (they involve denominators and the greek alphabet and are PITA to type out), at a depth of 330ft(100 m) and moving your arm at 3 ft/sec, the dynamic pressure is in the order of magnitude of 0.14 feet of head or 0.04% of the depth. Even assuming you could move your arm at 20 ft/sec (14 mph!) the dynamic pressure is only about 6.2 feet of additional depth (<2%)."

So with this we can conclude that the Dynamic pressure is normaly a small force for a diver and do not limit your watch capacity very much. It only reduces it whit a couple of meters at most.

So what can we conclude:

The Standardisation does not indicate a watch maximum capacity.
The rating is given by the manufacturer mostly due to marketing reasons and often the maximum capacity of a watch is seldom tested.
The difference between different watches with the same rating can be huge....
Dynamic Pressure is mostly just fear mongering and a myth

Sorry for this very lenghty post but hopefully I have thought you guys something new.....