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As we like to chuckle about now, Y2K ended up being a bit of a yawn. But do you recall the year 2000’s other calendar-based tech issue, the Leap Year Bug? Ultimately, it didn’t result in any major catastrophes either, but it did require additional foresight from programmers.

The concept of a leap year dates back to Julius Caesar, who added a day to the calendar every four years to account for the fact the Earth actually takes roughly 365.2421 days, not 365 days, to orbit the sun. The Julian calendar took effect in 46 BCE. The caveats came from Pope Gregory XIII in the year 1582, attempting to adjust for the fact the added day is slightly more compensation than needed.

Everyone knows an extra day gets tacked on to February every four years — you might not know there are some caveats associated with that. Years divisible by 100 are not leap years, unless the year is divisible by 400. So, the years 1700, 1800, and 1900 were not leap years, but 2000 was and so was 1600 before that. So, if any programmers knew the divisible-by-100 rule, but not the divisible-by-400 exception, they programmed for their software to skip Feb. 29, 2000.

Leap year trips up programmers every time

In 1996, Arizona lottery ticket sales were thwarted, a UK hospital found itself with equipment that didn’t function, and a taxicab company in Queens began charging higher fares a day early.

No major reports exist related to leap year-related errors in 2000, which could be due to the work of the President’s Council on Year 2000 Conversion. After a successful Y2K, the council continued its operations until March 2000 to ensure that developers made it past leap year error-free.

The government agency led by John A. Koskinen became aware of the potential blind spot in the tech community while preparing for Y2K. The council found some programmers had inadvertently programmed correctly for 2000’s leap year, being unaware of the divisible-by-100 rule.

Photo: Bychykhin Olexandr / Shutterstock

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Kate Johanns

Posted by Kate Johanns

Kate Johanns is a communications professional and freelance writer with more than 13 years of experience in publishing and marketing.

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