The time during which CRT (cathode-ray tube) electron beams return from the end of one line to the start of the next when in rasterscan mode. The return of a scanning beam to the starting point after completing a line or a frame is called fly-back
. Fly-back time is expressed in ns (nanoseconds, or one-billionth [10−9
] of a second) or μs (microseconds, or one-millionth of a second) for each fly-back period.