"Time: what one reads off clocks".

A good example of book design is this slim volume, beautifully laid out in small format, and perfect for the pocket when travelling. And the content is as good as the cover promises!
In 1905 the young Albert Einstein, an unknown patent clerk in Basle, published five extraordinary papers in rapid succession in Annalen der Physik. The fourth paper, on the 'Electrodynamics of Moving Bodies' ('Zur Elektrodynamik bewegter Körper') laid the foundation for Special Relativity.
The implications of science can never be completely foreseen. Special relativity predicts that a clock on a satellite such as used for global positioning will run ahead of the same clock on earth. Such is the accuracy of a modern atomic clock that these tiny differences can be precisely measured. If uncorrected, over six hours the difference would amount to five millionths of a second!
A tiny difference that translates to a positioning error of one kilometre, making all satellite navigation systems useless.

'Time: what one reads of clocks'. Subtle.

Special Relativity by Domenico Giulini, Oxford University Press, 2005