As several of your correspondents have said, all we are celebrating is numerology anyway. From a Christian perspective it is all a load of shoe repairers. The mystery of the Incarnation does not depend on the date being right.
Stuart Russell (letter, 27 December) is right that a person is aged one at the end of year zero, 100 at the end of year 99 and so on. The trouble is that there was no year zero. The Common Era did not begin on 1 January 000 - who would call it that?
So when the sixth-century cleric Dionysius Exiguus derived the numeration system that we all use today, he started with Year One. The first year was completed at the end of Year One, the first millennium at the end of year 1000, and so on.
The confusing fact that in the sixth century people believed that Our Lord was born in the previous year (now known as 1BC), does not make it count as Year Zero either; it is how Dionysius started that is important.
Now can we please all get some sleep?
Keighley, West Yorkshire