Excellent discussion on BBC 4's In Our Time with Melvyn Bragg on the history of time measurement.
<<Melvyn Bragg and his guests discuss the measurement of time. Early civilisations used the movements of heavenly bodies to tell the time, then mechanical clocks emerged in Europe in the medieval period. For hundreds of years clocks were inaccurate but now atomic clocks are capable of keeping time to a second in 15 million years.>>
stream, download or podcast In Our Time