Field rate
The field rate of an interlaced video image is twice the effective frame rate
Frame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...

, since interlacing draws only half of the image (the odd- or even-numbered lines) at a time. For example, a field rate of 60 Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

 will correspond to a 30 frames-per-second moving picture. A field rate can apply to either a video signal, or to a monitor designed to display that signal without conversion.

Theoretically, an interlaced signal could have three or more fields per frame, resulting in a field rate that is a 3x or higher multiple of the frame rate. However no such signal is in common use today.

Progressive scan monitors do not have a field rate, however they may still display interlaced video by converting each field into a full frame, a process called deinterlacing
Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....

. In this case, the monitor's frame rate would then likely match the video signal's field rate.
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