Set your watch by it, Edinburgh Castle, Edinburgh, Scotland. The purpose of this gun, fired at precisely one o'clock each day from the ramparts of Edinburgh Castle, is not, as some would have it, to startle the tourists (although it does accomplish this as well).

The gun, installed here in 1861 and connected electronically to the Calton Hill Observatory, was used to help ships in the Port of Leith adjust their clocks (critical for accurate navigational calculations).

Today its firing is purely ceremonial, and guaranteed to scare the haggis out of anyone not expecting its lunchtime blast.