I'm one of the dwindling band of pedants who believe the end of the second millennium is properly the end of the millennial year 2000. But I'm also a practical person about most things and I know a lost cause when I see one.

So I guess I'll celebrate with everybody else as 1999 counts down to midnight, and try not to make a nuisance of myself. If, like me, you're curious about how we got into this pickle, you may enjoy, as I did, a little book by Stephen Jay Gould, "Questioning the Millennium: A Rationalist's Guide to a Precisely Arbitrary Countdown. "When will it happen? Logic dictates one answer, popular opinion the other, Gould says - and clearly, popular opinion is going to win.

By any measure derived from natural intervals like days, months and years, there's nothing special about the year, whichever it is, that we designate as the millennium. If our number system were binary, like a computer's, or based on 12 like the Babylonians' or 20 like the Mayans', some other year would end in lots of zeros.

It also matters when the year-count began. Though our current dates are tagged A.D. for anno Domini, in the year of the Lord, no one in the year now known as A.D. 1 had any reason to call it that. The 6th century monk who worked out the chronology, Dionysius Exiguus, decided that Jesus was born in the year 753 A U C. (ab urbe condita, meaning from the founding of Rome).

Just a couple of little problems. One is, he didn't get the date right. "Herod died in 750 A U C ," Gould says. "Therefore, if Herod and Jesus overlapped (and the gospels will have to be drastically revised if they did not) then Jesus must have been born in 4 B.C. or ear-lier."

Dionysius' other little problem was that zero hadn't been invented yet, so he didn't put it in, and that led directly to our confusion over the century. Your car's odometer doesn't get confused, because it reads 0 miles for the first mile.

Dionyisus' first mistake tripped up another chronologist, Archbishop James Ussher of Ireland. Ussher was working in a theological tradition that held the age of the Earth corresponded to the six days of creation, and that each day was a thousand years in the sight of God. The birth of Jesus was the dawn of a new age, so also the dawn of a new day, and therefore must have happened exactly 4,000 years after the moment of creation. So in 1650 he announced that the creation had occurred, precisely, at noon on Oct. 23, 4004 B C. . . .

If you believe that the apocalypse will come at the end of the sixth day, you will therefore be relieved to know that the time of peril passed quite unremarkably on Oct. 23, 1996, or maybe 1995, depending on what you want to do with the missing year 0.

Our century's principal worry about the year 2000 is whether old computers will go haywire because they've been programmed to think the year '00 means 1900. But were our ancestors a thousand years ago panicked about a theological rather than a cybernetic apocalypse?