Time signal
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A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.
These automatic signal clocks were synchronized by telegraphy in 1905 before the widespread use of radio
A RBL 40-pounder Armstrong gun being fired as "the one o'clock gun" on Woolwich Common, circa 1905
The time ball on the roof of Greenwich Observatory, London
A modern LF Radio clock
9 O'Clock Gun
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The 9 O'Clock Gun is a cannon located in Vancouver, British Columbia, Canada, that is ordinarily fired daily at 21:00 PT.
The 9 O'Clock Gun firing in June, 2006
The 9 O'Clock Gun firing in May 2017
Plaque at the 9 O'Clock Gun.
A closer view of the gun.