Citizen's Challenge Timer, released in 1972, was the brand's first watch with a proper chronograph function — a genuine technical milestone. But it was the variant that followed just months later, in January 1973, that people actually remember: a "bull-head" case design with the crown and pushers relocated to the top, giving the watch a distinctive silhouette that earned it the nickname "Tsuno Chrono," from the Japanese word for horn.
This AN3660-81A is a modern continuation of that design rather than a strict historical reissue — quartz-powered, 38mm, with a 1/1-second chronograph and the same bull-head pusher arrangement that made the original stand out on wrists in the 1970s. Half a century later, the silhouette still reads as unmistakably its own thing on a crowded shelf of chronographs.
