Lord George Murray, inspired by reports of the Chappe semaphore, proposed a system of visual telegraphy to the British Admiralty in 1795. He used rectangular truss towers with six five-foot octagonal shutters on horizontal axes that could be switched between horizontal and vertical positions to give signals.
Mechanics’ Magazine and Journal of Science, Arts, and Manufactures – Google Books.
A detailed description of how it works has not been handed down. Only the description listed here exists, from which an attempt was made to derive a coding.
The first attempt by Helmar Fischer has gained acceptance in the geocaching scene; however, it is flawed.
Details can be found at Transferring information – not with the big flap but with six small flaps … der Klappentelegraph | (sachsen.schule)
Another source is Omer Roucoux with his contribution Dunstable Signalling Station: Page 2 – Digitised Resources – The Virtual Library (culturalservices.net)