As a result, his determination of the birth year of Christ was apparently off by about 4 years, but the error was not realized until centuries after the system had come into general use, leading to the strange circumstance that Christ was actually born in approximately 4 BC.
The designations BC and AD deserve a brief explanation at this point.
Using a star as a power source, an array of collectors on one side of the planet would gather dark energy in stages, redirecting it to the planetary core, where it was held in place by the natural magnetic field of the planet, as well as an artificial containment field maintained by the machinery the First Order had installed within the crust.
A colossal hollow cylinder, large enough to dominate the view of the planet from orbit, penetrated the containment field to a predetermined distance, in order to direct the blast towards its target, and also to absorb its energy, which would otherwise cause catastrophic groundquakes.
This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, and BC denoting years before the start of the era.
There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC.
For decades, it has been the unofficial global standard, adopted in the pragmatic interests of international communication, transportation, and commercial integration, and recognized by international institutions such as the United Nations.
However, BC is placed after the year number (for example: AD 2017, but 68 BC), which also preserves syntactic order.
The number system used throughout the modern world is a fully place-valued decimal system.