In the 1920s, 78.26 rpm was standardized when stroboscopic discs and turntable edge markings were introduced to standardize the speeds of recording lathes. At that speed, a strobe disc with 92 lines would "stand still" in 60 Hz light. In regions of the world that use 50 Hz current, the standard was 77.92 rpm (and a disk with 77 lines). After World War II, these records became retroactively known as "78s", to distinguish them from the newer disc record formats known by their rotational speeds. Earlier they were just called "records", or when there was a need to distinguish them from cylinders, "disc records".