A watch may be claimed to be waterproof when it is able to resist sweat, sprayed water (e.g. during hand washing), and rain. Additionally, no humidity may be allowed to penetrate into a waterproof watch during a 30 minute immersion in water with a depth of 1 meter. A waterproof watch that fulfils these requirements is appropriate for normal use, but it should only be worn in conditions that preclude major variations in water pressure and temperature. For this reason a water-sports enthusiast should inform his or herself well concerning the robustness of a new watch before deciding to buy it. For anyone that spends a lot of time in the water – who swims, dives, sails or windsurfs – it makes good sense to invest in a proper diver’s watch. In the watch industry there are many who use verbal tricks like printing ‘30m’ on the watch face to give the impression that the watch is watertight to a depth of 30 meters. In fact they have done nothing more that print ‘30m’, which could mean anything.
A ‘world-time’ watch shows the actual time in some or all of the 24 time zones of the Earth. It does this with the aid of sub-dials or with the aid of a scale on the edge of the facia.