leap second

• an extra second added to added to Coordinated Universal Time (UTC)
when the difference between UTC and Universal Time (UT) approaches 0.9 seconds.

This becomes necessary because Coordinated Universal Time,
based on International Atomic Time (TAI), using atomic clocks,
is more accurate than Universal Time (UT), based on the Earth's rotation.
The two systems get too much out of sync and need to be corrected.

EXAMPLE: