If someone told you you could own a wrist watch which was accurate to 1 second over 1,400,000 years, never needed a battery, but received it's working power from light,  for under $100-would you believe them?  I wouldn't, but it's true. (I payed less than $60 on Amazon before the price increased)  Casio's Waveceptor Atomic timekeeping receives a radio signal  transmitted from the Cesium Atomic clock in Fort Collins, CO.  The Cesium Atomic clock is accurate  to one second in 1,400,000 years!  (Granted, if you travel to distant lands frequently, this is not the watch for you.) The watches battery is automatically charged by light, either direct from the sun or from light sources inside.  I always know I'm the guy in the room with the most accurate watch.  Oddly, guys with Rolex , Tag Heuer or other pricey watches don't like me reminding them of that?