One thousand five hundred years ago, the philosopher Aurelius Augustus when asked to define time, said: "If someone asks me, I know. If I wish to explain it to someone who asks I know not."

That situation hasn't changed much today. Time remains a teasing conceptual barrier, elusive and indefinable. Nonetheless, countless men over the centuries have devoted their lifetimes measuring it with ingenious devices.

From the simple stick in the ground showing Babylonians time, to the first calendar in China, from the waisted glass vessel filled with fine sand measuring time in hours to the early lamp oil clock, from the famous Konark Wheel Temple of Orissa, to the 16th century Jantar Mantar Astronomical Observatory in Jaipur - the first in the world to the early 18th century Greenwhich Observatory, to the famous 23 feet diameter Big Ben Clock installed in 1859 in London that can be heard miles away, to the auxiliary sphere system representing the position of various planets, to the present day cesium automatic clock which splits the second into 10 billion parts... Timekeeping has always been striving for accuracy. The minute was measured for the first time in the 17th century. The second and its sub-divisions followed. Today, space-age technology routinely makes use of the nanosecond, a thousand millionth of a second.

When will it all end? Will there ever be a final perfect timekeeper to end all timekeepers? And, more fascinatingly will somebody in the distant future be able to ultimately define what Aurelius Augustus couldn't?

Only time will tell.