NEW DELHI: A 'leap second' was added to the Indian clock at 5:29.59 hours today to synchronise with the Earth 's rotational clock. As the atomic clock at National Physical Laboratory struck 23:59:59 last night, it was programmed to add an extra second to 2017 to compensate for a slowdown in the Earth’s rotation.Adding a second barely has an impact on daily life but matters in satellite navigation, astronomy and communication.