nit picking? depth ratings on watches

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sandanbob

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Good morning!

This is a small thing, I know, but something I have thought about for some time.

What might I be missing?

Here it is- some watches are labeled that they are rated to 200 meters/660 feet, and 20 atm. Wouldn't 200 meters/660 feet be 21 atm? And, the inverse- wouldn't 20 atm be more like 627 feet/190 meters?

I know in a practical sense that it won't make a difference, but it's just something that seems not quite right.

Thanks!

Bob
 
The difference between atmospheres gauge and atmospheres absolute. 20 atm gauge is 21 ATA (atm absolute).
You think that's what they are doing? Using gauge instead of absolute? Could be.
 
That is what the watch experiences. It’s manufactured and sealed at one ATA, so the experienced pressure differential at one ATA is zero.
 
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https://www.shearwater.com/products/teric/

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