When the clocks struck midnight on Friday, 31 December 1999, there could have been few educated people who did not realize that the twenty-first century would not begin for another year. For weeks, all the media had been explaining that because the Western calendar started with Year 1, not Year 0, the twentieth century still had twelve months to go.

It made no difference; the psychological effect of those three zeros was too powerful, the fin de siècle ambience too overwhelming. This was the weekend that counted; 1 January 2001 would be an anticlimax, except to a few movie buffs.

There was also a very practical reason why 1 January 2000 was the date that really mattered, and it was a reason that would never have occurred to anyone a mere forty years earlier. Since the 1960s, more and more of the world’s accounting had been taken over by computers, and the process was now essentially complete. Millions of optical and electronic memories held in their stores trillions of transactions—virtually all the business of the planet.

And, of course, most of these entries bore a date. As the last decade of the century opened, something like a shock wave passed through the financial world. It was suddenly, and belatedly, realized that most of those dates lacked a vital component.