Smart clock: a new time

A tutorial description is given of the smart clock, which makes it possible for any clock to be automatically synchronized to an external standard with a minimum of measurements. The concept covers a range of applications from wrist watches and household clocks to the specialized world of high-accuracy clocks. The smart clock enhances the accuracy or stability of a clock or oscillator by characterizing it against an external standard. The smart clock algorithm uses optimal estimation and prediction to apply a correction to the output of the oscillator, maintaining any combination of time or frequency accuracy or stability within specified limits. The algorithm decides when external measurements are necessary to maintain the desired accuracy or stability. An example of how the smart clock could be used to maintain a simple clock to 1 s using measurements over the telephone lines is given.>