I believe that FF let air molecules in - its unlikely that there was any He present in that dry dive chamber. Nitrogen and oxygen may have another electron shell, but they're not that much bigger than Helium is in terms of mechanical watches (He diameter approx 1 angstrom, N diameter approx 1.5 angstrom). Thats why it causes me to re-assess: if the seals on a watch at 5 atmospheres can't hold out helium or the somewhat larger oxygen and nitrogen, then maybe its a good thing to have a valve afterall.
I had to look it up, but an angstrom is a ten-billionth of a meter.
Last edited by namor; 05-07-2012 at 12:21 PM.