A variation of the omega wrap, such as that used by Echo Science Corporation of Mountain View, California in its instrumentation and high resolution video recorders in the late 1970s and 1980s, wraps the 1-inch tape about 190 degrees around the two-headed drum, so there is signal overlap between the two heads. Head switching in video recorders occurs instantaneously in the video models, during a horizontal sync interval. With a standard NTSC video signal a head can cover one sixth of a field each time it passed across the tape. Switching in instrumentation models is gradual, so the signals from both heads overlaps briefly, producing a transient-free output signal where the original signal does not contain convenient dead intervals during which a switching transient can be hidden.