Time has been kept locally
for thousands of years, as long as we have been keeping track of time, from the
days of shadows and sundials. When the sun is at its highest point, call
it noon. When portable timekeeping came into play, in maybe the 1500s,
when traveling, those portable clocks had to be reset for local time at every
location. That wasn’t much of a problem until the late 1800s; that’s when
trains came into popular usage. Every location keeping track of its own
time didn’t really work for train schedules, so time zones were
instituted. Divide the globe into 24 roughly equal one-hour slices and
there we have it. At the sun’s highest point in the sky, in the middle of
each zone, it will be noon (roughly). East and west of center, in every
time zone, noontime won’t correlate exactly with the clock, it will be plus or
minus a rounding error. Close enough.