In the discrete model of time, a time-line clock is a set of
physical clocks coupled with some specification of when each physical
clock is authoritative. Each chronon in a time-line clock is a
chronon (or a regular division of a chronon) in an identified,
underlying physical clock. The time-line clock switches from one
physical clock to the next at a synchronization point. A
synchronization point correlates two, distinct physical clock
measurements. The time-line clock must be anchored at some chronon to
a unique physical state of the universe.