It was used by Chronometers on ships as a sync event. Earlier they had put up a time ball on Canton Hill but that could not be seen by sailors due to fog. Note

It was used by Chronometers on ships as a sync event. Earlier they had put up a time ball on Canton Hill but that could not be seen by sailors due to fog. Note: The gun is fired at 1pm because they have to fire it just once thus saving cost. Other ideas were considered such as firing it 9 times at 9pm.