Geoff Alves is absolutely wrong in stating that the millennium begins on January 1, 2001 (letter headlined, 'False dawn', South China Morning Post, June 15).
In the Gregorian calendar, dates are calculated backwards (BC 'before Christ' or BCE 'before Common Era') and forwards (AD 'anno Domini' or CE 'Common Era') from year one (an assumed date of the birth of Jesus).
The first AD year began on January 1, 0000, and ended on December 3 of that year, although for obvious reasons the first positive number is used to denote this first year.
Hence whenever 1 AD is written, it denotes an entire year as opposed to meaning the first day of that year. Only if the latter were true would the third millennium begin on January 1, 2001.
By these calculations, the second year ended on December 31, 0001, the third year ended on December 31, 0002, and so on.
This is the only correct method of calculation, after all, anything is one year old only upon completion of its first year and not upon its commencement of that year.