The flap display was invented in 1948 by a self taught engineer named Remigio Solari. His flap display can do numbers and letters.
It was renamed The Solari Board, and first installed in 1956 in Belgium at Liege-Guillemins station. It was such a success to display time and information, that it became industry standard used in places like railroads and airports worldwide.
The clock version was made by Gino Valle, an Italian architect in the 1950’s. It would have a constantly spinning motor, with gears to move each shaft at the correct time to flip a leaf down.
Flip clocks can not operate backwards, you need to turn it 23 hours ahead to go back 1 hour during daylight savings.
Solar brand flip clock Model CL90 with AM/FM Radio and Alarm.