ABSTRACT
Introduction So far in our discussion of timekeeping something has been missing. We have seen how time scales are based upon the rotation of the Earth or the movements of the Sun, Moon and planets. Yet when it comes to practical matters, we do not glance at the sky to find out if it is time for lunch or to fetch the children from school. That is why we have clocks. The traditional purpose of a clock was to subdivide the mean solar day into the more convenient intervals of hours, minutes and seconds. Every now and then the clock would be adjusted to mean solar time by comparing it with a better clock, which ultimately derived its time from signals emanating from astronomical observatories which computed the time from measurements of the stars.
