|Sometimes your VCR misses the beginning
of a program because the VCR's clock has drifted a little. If the
VCR's clock is a little slow, the VCR comes on a little late. And
sometimes your bedside clock sets off its alarm a little too late to hear
the beginning of the morning news. You have to overcome this little
electronic foible by setting your clock or the alarm to be a little fast.
But some electronic clocks are remarkably precise and accurate.
Old fashioned analog electric clocks were precise because they are synchroous motors designed to rotate precisely at the speed of the generators that produce the alternating current, and the generators are kept running at a precise 60 cycles per second by comparing their output with scientific time standards. Time standards are among the most precise measurements that humans can accomplish.
Our wrist watches aren't connected to the alternating current power grid and so must generate their own accurate frequency standards. They use precisely ground pieces of quartz crystal which can be made to vibrate under the influence of an electrric field. (The quality of quartz that let's this happen is called "piezoelectricity," a connection between strain and electric charges at the crystal's surface, and a characteristic of very few materials other than quartz--it incidently seems to be what causes silicosis, a serious disease of the lungs resulting from breathing finely ground mineral dust.)
Plug-in digital clocks usually have
quartz crystals to control their time-keeping, but a few count the cycles
of the alternating current. For modern computer technology this is
a trivial task and results in vastly superior time-keeping.
Here is a difference in clocks that very few people notice, but a difference that could help us avoid missing accurately timed events. Understanding how things work can improve our ability to anticipate the outcomes of what we do.