The ancients recorded the years with dry branch. Methyl, ethyl, propyl, butyl, pentahexyl, hexyl ,nonyl ,and decyl  are ten dry, also known asTiangan.Zi,Chou,Yin,Mao,Chen,Si,Wu,Wei,Shen,You,Xu,Hai was already 12 branches, also known as the Earth Branch.In turn, the dry days are used to distribute the branches of the earth, such as Jiazi, Yichou and Bingyin,,, Gui you, Jia xu, Yi hai, Bing zi, etc., are repeated every 60 years, commonly known as sixty Huajiazi. According to the chronology of the stem and branch, the year 2014 is the year of Jia Wu, and the year 2015 is the year of Yi Wei.
Modern people no longer need to keep dry branch to recorded the years can be derived from the above statement.