How much does watch accuracy vary, and why?
At least in theory, we all should be Johnny-on-the-spot synchronized. Starting in the early 1970s, the advent of battery-powered quartz wristwatches gave ordinary folks access to a timekeeping technology that once was available only to scientists and technicians [source: NMAH]. Basically, if you apply electricity to a tiny piece of quartz and then bend it, the crystal will give off a relatively constant electrical signal that can be used to operate an electronic clock face [source: NIST]. By the early 2000s, quartz watches had become so popular that mechanical watches had been reduced to just 13 percent of the global watch market [source: IEEE].
But consumer-grade quartz watches aren't totally precise. Remember, we're talking about relatively cheap miniature devices that are churned out rapidly in vast quantities in factories -- not some multi-million-dollar gadget custom built for a lab. Even the most expensive quartz-crystal watch in the jewelry store still relies on a mechanical vibration whose frequency can be affected by a variety of factors, including a crystal's size and shape. No two quartz crystals are exactly alike, which can lead to at least a slight discrepancy between two watches from the same assembly line [source: NIST]. Additionally, watches' precision can be affected by external factors, such as temperature and humidity, and by wear and tear that affects the stability of the tiny motors inside them, which generate the electric field to which the crystals are exposed [source: Lombardi].
The upshot is that quartz watches tend to become slightly less accurate over time -- with a great deal of emphasis on "slightly." Chronocentric.com, a Web site for timepiece enthusiasts, estimates that consumer-grade quartz watches typically lose between a tenth of a second and two seconds per day -- a discrepancy that, if left uncorrected over long periods, could lead to a watch being off by a few minutes [source: Chronocentric.com]. A study published in Horological Journal in 2008, however, suggests that at least a few cheap watches are vastly more accurate. Researchers, who looked at humble timepieces that included a counterfeit Rolex purchased from a street vendor for $15 and a $30 discount store Timex, found they were all accurate to within a few thousandths of a second per day. It would take years for such a shift to become noticeable to their owners [source: Lombardi].