Curious Curaçao Clock

No, this isn't a photo from the current focus of my analytical series, Fischer - Tal, Bled 1961. It's a photo of the same players taken at Curaçao 1962. What caught my attention wasn't the image of the two World Champions, future and former at the time of the photo. It was the clock they are using.

The clock has a wire coming out the back and two wires connected to the sides. I can't remember ever seeing a chess clock like that. The photo is from page 132 of 'Curaçao 1962' by Jan Timman. The same clock is shown on the cover of the book: Curacao 1962: The Battle of Minds that Shook the Chess World (Amazon.com; click 'see larger image'). I assume it was used to drive the clocks beneath the demonstration boards, also visible in the photo.