Semaphore Clock

A semaphore clock is a visual representation of the standard semaphore alphabet (with flags held at arm's length), in which the arms are replaced by the hands of an analog clock.

Each hand represents an arm oriented at a specific angle on the clock face.

Each letter is associated with a pair of angles formed by the hour and minute hands. The correspondence table is:

A		B		C		D		E		F		G
H		I		J		K		L		M		N
O		P		Q		R		S		T		U
V		W		X		Y		Z
dCode.fr

Decoding a semaphore clock involves precisely identifying the angular position of each hand (theoretically a multiple of 45°) in order to convert these positions into standard semaphore via the correspondence table above.

Note: The minute and hour hands can be reversed without affecting the decoding.

Each position is a multiple of 45° (approximately 1.5 hours for the hour hand or 7.5 minutes for the minute hand on a standard clock face).

Most real clocks have an hour hand that moves continuously (not in discrete jumps), so a semaphore clock can display inconsistent positions from a timekeeping perspective (the hour hand is not perfectly aligned with its theoretical position).

The hands of a semaphore clock do not indicate the actual time, which can result in implausible times (to be analyzed according to the context).

A classic mechanical clock can serve as a semaphore if the hour hand moves in discrete jumps (and not continuously).

Several systems use coded visual configurations:

— Maritime semaphore: two flags held at arm's length, forming angles corresponding to the alphabet.

— Chappe optical telegraph: articulated arms mounted on towers, visible from a distance.

— Visual Morse code: light signals corresponding to sequences of dots and dashes.