The first is by
the reigns of the Emperors. That is to say, the first year of a
sovereign's reign--reckoning from the New Year's day following his
accession--became the 1 of the series, and the years were thenceforth
numbered consecutively until his death or abdication. This method
might be sufficiently accurate if the exact duration of each reign
were known as well as the exact sequence of the reigns. But no such
precision could be expected in the case of unwritten history,
transmitted orally from generation to generation. Thus, while
Japanese annalists, by accepting the aggregate duration of all the
reigns known to them, arrive at the conclusion that the first
Emperor, Jimmu, ascended the throne in the year 660 B.C., it is found
on analysis that their figures assign to the first seventeen
sovereigns an average age of 109 years.

The second system was by means of periods deriving their name (nengo)
from some remarkable incident. Thus, the discovery of copper in Japan
was commemorated by calling the year Wado (Japanese copper), and the
era so called lasted seven years. Such a plan was even more liable to
error than the device of reckoning by reigns, and a specially
confusing feature was that the first year of the period dated
retrospectively from the previous New Year's day, so that events were
often recorded as having occurred in the final year of one period and
in the opening year of another. This system was originally imported
from China in the year A.D. 645, and is at present in use, the year
1910 being the forty-third of the Meiji (Enlightenment and Peace)
period.

The third system was that of the sexagenary cycle. This was operated
after the manner of a clock having two concentric dials, the
circumference of the larger dial being divided into ten equal parts,
each marked with one of the ten "celestial signs," and the
circumference of the smaller dial being divided into twelve equal
parts each marked with one of the twelve signs of the zodiac. The
long hand of the clock, pointing to the larger dial, was supposed to
make one revolution in ten years, and the shorter hand, pointing to
the small dial, revolved once in twelve years. Thus, starting from
the point where the marks on the two dials coincide, the long hand
gained upon the short hand by one-sixtieth each year, and once in
every sixty years the two hands were found at the point of
conjunction. Years were indicated by naming the "celestial stem" and
the zo