This evening, clocks around the world are gaining an extra second. A so-called leap second will tonight, June 30th, right before 8 p.m. Eastern Daylight Time, or midnight Coordinated Universal Time/Greenwich Mean Time. Why? Precision, in short. Without such a correction, time reckoned by Earth's rotation drifts away from atomic time because of irregularities in the Earth's rate of rotation, writes Wikipedia.
Precision. If youre a high-frequency trading firm, you can lose alpha when trading. Adding a leap second back in the 1990s wasnt a big deal but with the spread of HFT and low-latency data delivery systems, an entire second lost could be a very big deal to financial markets around the world.
This change is happening right when after-hours markets in the U.S. are under way and a sample of Asian markets are just opening for business.
Thankfully, like Y2K, todays modern exchanges have plans for the extra second to the business clock.
The London Stock Exchange will not be open during the leap second. Remain calm and carry on.
