A horizontal sundial is built on one side of the brass disc. It consists of an engraved dial and a shadow projector, which must be aligned in a north-south direction. The following is engraved above the Roman numerals of the sundial: "DEREPAS PALAIS ROYAL No 24 A PARIS" (location of the original). On the right is engraved: "Siersburg WOZ" (this sundial was calculated by Mr. Philippi for this Saarland location).
The magnifying glass is aligned so that the powder in the cannon is ignited when the sun passes through the zenith.
When the noon gun banged, the hands of the wheel clocks were set vertically - 12 noon.
When the cannon ignited at Forbach Castle, the people of Saarbrücken heard the bang and knew it was time for lunch.
Image source: United Features Syndicate Inc.
In Nice (France) the gunshot at noon has been a tradition since 1860. The Arte-TV film on the next page lasts 6:30 minutes (in German).
In contrast to the 12 p.m. firecracker, the time signal at the Flamsteed House of the Royal Observatory in Greenwich is at 1 p.m. GMT (Greenwich Mean Time - today UTC) since 1833, or in summer at 1 p.m. BST (British Summer Time).
At 12:55 the ball rises halfway, at 12:58 to the top, and at 1:00 it falls.
Video: Youtube 39 seconds