@chu Quartz timepieces use a crystal oscillator, which has an exceedingly precise and regular frequency, combined with electronics that count the oscillations, to measure time. This is an order of magnitude or more better / more accurate than purely mechanical solutions that preceded the technology. The technique only became available at a size and price point that made it useful in most people's watches over the past 40 years or so, so it's relatively new as watch technology goes.