A loud boom and a cloud of smoke occur every day (except Sunday) at 13:00 hours at this vantage point atop the Edinburgh Castle Grounds, allowing citizens and visitors to check their clocks and watches. The origin of the tradition lies in the days when sailing ships in the Firth of Forth were able to check and reset their chronometers in the days before acurate timepieces were available. Today it is a highlight for castle visitors - just after one p.m., the crowds disperse a bit for lunch!