Periodic table (detailed cells)
Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869. Mendeleev invented the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
Dionysius Exiguus' Easter table
Dionysius Exiguus's Easter table was constructed in the year 525 by Dionysius Exiguus for the years 532–626. He obtained it from an Easter table attributed to Patriarch Cyril of Alexandria for the years 437–531. The latter was constructed around the year 440 by means of extrapolation from an Alexandrian Easter table constructed around the year 390 by Patriarch Theophilus of Alexandria. The great historical importance of Dionysius' Easter table is twofold: