It is still very common in Taiwan to date events via the republican era.The People's Republic of China adopted the common era calendar in 1949 (the 38th year of the Chinese Republic).1840 (MDCCCXL) was a leap year starting on Wednesday (dominical letter ED) of the Gregorian calendar and a leap year starting on Monday (dominical letter GF) of the Julian calendar, the 1840th year of the Common Era (CE) and Anno Domini (AD) designations, the 840th year of the 2nd millennium, the 40th year of the 19th century, and the 1st year of the 1840s decade.As of the start of 1840, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1918.The epoch moment or date is usually defined by a specific clear event, condition, or criterion — the epoch event or epoch criterion — from which the period or era or age is usually characterized or described.
The "epoch" then serves as a reference point from which time is measured.
In astronomy, an epoch is a specific moment in time for which celestial coordinates or orbital elements are specified, and from which other orbital parametrics are thereafter calculated in order to predict future position.
A similar system existed in China before 1912, being based on the accession year of the emperor (1911 was thus the third year of the Xuantong period).
With the establishment of the Republic of China in 1912, the republican era was introduced.
Time measurement units are counted from the epoch so that the date and time of events can be specified unambiguously.
Events taking place before the epoch can be dated by counting negatively from the epoch, though in pragmatic periodization practice, epochs are defined for the past, and another epoch is used to start the next era, therefore serving as the ending of the older preceding era.