For those who believe that in the good old days -- before calculators, before computers -- people were better at mental arithmetic, The Times offers a sobering New Year's message: Not necessarily.

On Feb. 6, 1898, it seems, someone preparing the next day's front page tried to add 1 to the issue number in the upper left corner (14,499) and came up with 15,000. Apparently no one noticed, because the 500-issue error persisted until yesterday (No. 51,753). Today The Times turns back the clock to correct the sequence: this issue is No. 51,254.

Thus an article on March 14, 1995, celebrating the arrival of No. 50,000 was 500 days premature. It should have appeared on July 26, 1996.

The error came to light recently when Aaron Donovan, a news assistant, became curious about the numbering, which he updates nightly when working at the news desk. He wondered about the potential for self-perpetuating error. Using a spreadsheet program, he calculated the number of days since The Times's founding, on Sept. 18, 1851.