On Jan 19, 7:15 pm, Red wrote:
....
I take it he meant that it may be there to release pressure *inside* the
case to keep the case from "exploding" in a low pressure environment,
not imploding as would be the case of external pressure when sinking.
Red

Yes, that's exactly what I was trying to say. It is a curious feature
and I'm just speculating about its purpose. Maybe it's for something
else.

-- Tom.