Many Worlds, Many Calendars 

What is the Y2K problem?

Y2K is computer-speak for Year 2 Thousand (2000 A.D.) because a "K" stands for a thousand kilobytes.

To save space, computer programmers in the 1960s began using only two digits for the year. Thus 01/01/98 was January 1, 1998. But when the computer sees 01/01/00 it thinks the year will be 1900. So what's wrong with that?
The same thing that was wrong with the Julian calendar--getting the number of days wrong every hundred years. The Julian calendar made every century year--1200, 1300, 1400--a leap year. This system kept adding a day too many over and over again.
One day every hundred years may not seem like a lot because most of us never even live a hundred years.  But after just a couple of centuries, the calendar is already off by two whole days. After 4 centuries it is off by four days, and after seven centuries it is wrong by a whole week.

In the 1200s Muslim scientists on the Iberian peninsula figured out the way to match up the solar calendar with the sun. They made a leap year only in century years that could be evenly divided by 400. So 1200 was a leap year but 1300 was not. 2000 is a leap year, but 1900 was not.
2000 is a leap year, but 1900 was not. And that is the whole problem. 

So unless all our computers are reprogrammed, we won't be able to put February 29, 2000 on our dates. Airlines won't be able to schedule flights because computers won't allow the date. Banks won't be able to borrow money overnight, and won't be able to pay us the right amount of interest.
And if some computers have skipped February 29, 2000, all our computers could  be out of sync.  Some will think it is Tuesday when it is only Monday, or worse will think it's Monday when it is really only Sunday.

But in order to get the right latitude for every place on earth, scientists had to have their leap years right.

Measuring LatitudeHome page