The World Calendar Book, with a thickness of 2,180 pages, was made during the period 1984-2011. In the process of writing for the history of Xuan Pha village (Thanh Hoa), the author Do Thanh Lam discovered that the book "Yin and Yang changes the 2000 year calendar" with many false details, which leads to inaccurate timelines.
Since 1984, he has devoted much time and dedication to "finding the truth about calendar time." That is the reason for the birth of the world calendar of 3,240 years.
According to VietKings (Kyluc.vn)