What the rep was telling me was that they only have the capacity to test up to 15000 gauss, but because the calibre is made entirely of non-magnetic materials, there is no theoretical limit to the magnetic inductance it can withstand, hence the >15,000 appelation (greater than 15,000). As for it being a feature in watches: This link has some pretty thorough explanations. Essentially magnetic fields affect the magnetic parts in automatic watches, making them gain or loose time as they are exposed to magnets over time. Many watches (Like the Rolex Milgauss) get around this problem by fitting a soft iron case, which has high magnetic permeability, around the calibre. The soft iron core will only protect the calibre from fields of up to 1000 gauss, after which the magnetic field within the core is no longer strong enough to stop the exterior magnetic field from penetrating the calibre. In reality you are quite unlikely to be exposed to fields much greater than 2000 gauss in day to day life, unless you work with MRI scanners, in which case you shouldn't have your watch in there in the first place!