The bright red Time Ball on top of Flamsteed House is one of the world's earliest public time signals, distributing time to ships on the Thames and many Londoners. Please note: unfortunately the the Time Ball is currently not in operation, awaiting repairs due to damage from recent weather conditions.
The Time Ball was first used in 1833 and still operates today. Normally each day, at 12.55, the time ball rises half way up its mast. At 12.58 it rises all the way to the top. At 13.00 exactly, the ball falls, and so provides a signal to anyone who happens to be looking.
Of course, if you are looking the wrong way, you have to wait until the next day before it happens again. The time ball drops at 13.00 GMT during the winter months and 13.00 BST during the summer. Please note: the time ball will not operate if the weather is too windy.