Time Realisation (metrology)

1 time

1.1 direct measurement of solar time
1.2 timekeepers
1.3 time generators

time

the realisation of time has gone through 3 phases. during both first , second phases, man used solar time—during first phase, realisation of time observing earth s rotation using such devices sundial or astrolabe. during second phase actual timing devices such hourglasses or clocks used. if user needed know time-of-day rather elapsed time, clocks synchronized astronomical time. third phase made use of clocks sufficiently accurate measure variations in earth s rotation—such clocks taking on rotation of earth prime measure of time.

direct measurement of solar time

sundials , astrolabes

timekeepers

accuracy of clocks

time generators

radiation frequency & si