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Next Tuesday is going to be a longer day than the days before

The Computer Corner

By Charles Mille

When you wake up next Wednesday morning, July 1, if you discover some electronic device or another is not working, here is a possible explanation. Next Tuesday is going to be a longer day than the days before — exactly one second longer. Time kept by atomic clocks is constant, but the rotation of the earth is slowing down by about two milliseconds per day, so 25 times since 1972 there has been an extra second added to the length of the year in order to compensate. This happens every year or two, and every time this happens it seems to cause more chaos in cyberspace than it did the last time.

The last leap second in 2012 temporarily took down much of the Internet due to a bug in the Linux operating system used by many web servers. Since the leap second occurred at midnight, most of the problems were dealt with before Internet users in Western Europe and North America started their day.

Billions of embedded systems (cell phones, cash registers, thermostats, ATMs, etc.) all rely to one degree or another on accurate timekeeping. Different devices have differing tolerances for error, but precise time synchs can be important. For example, if you were planning a trip to the International Space Station and your GPS was one second off, you would only miss your rendezvous by 7.6 kilometers. Back on earth the error would be less, but you could still miss your freeway exit as you sped down the highway.

Simple embedded computer systems built into appliances are sometimes too dumb to even notice the time change, meaning that your alarm clock might be a second late or coffee maker might turn itself off one second early. More sophisticated computer systems know that a minute is supposed to have 60 seconds and not 61. Machines such as the robotic riveter on the automotive assembly line could mistakenly interpret the extra second as a potential danger condition and shut down the whole assembly line. Bookkeeping systems that are tied to exact time for billing purposes could go into a panic if they do not know how to bill for that extra second.

All of the unforeseen problems caused by the leap second have led for some to call for an end to the practice. The US wants to get rid of leap seconds because of the disruptions to precision timekeeping systems. Britain opposes the change because no more leap seconds would inevitably result in atomic time being several seconds offset from solar time. Of course, part of the reason for objections from the United Kingdom might be that since 1847 the entire world’s time has been based on Greenwich Mean Time, which is measured by the time at which the sun crosses above the Royal Observatory east of London.

As of this writing, the 2015 leap second is still scheduled to take place at midnight UTC on June 30. So, if you have nothing else better to do Tuesday night at 7pm Mexico time, you can pull up one of the many web sites that show the time of the atomic clock. At midnight it usually counts off the seconds 57, 58, 59, 00. Tuesday night it will count off 57, 58, 59, 60 and 00. You should be able to see it unless a large number of web sites on the Internet crashes again.

Charles Miller is a freelance computer consultant, a frequent visitor to San Miguel since 1981 and now practically a full-time resident. He may be contacted at 415 101-8528 or email FAQ8 (at)


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