Display system in which two interleaved fields are used to create one frame. The number of field lines is one-half of the number of frame lines. NTSC (M) systems have 262.5 lines per field. PAL (B, D, G, H, I) scan system have 312.5 lines per field. Each field is drawn on the screen consecutively, first one field, then the other. The field scanned first is called the odd field, the field scanned second is called the even field. The interlaced scanning system is used to prevent screen flicker. If frames were scanned on the screen without interlacing fields, the light level created by the first frame would decrease noticeably before the next frame could be scanned. Interlacing the fields allows the light level of the screen to be held more constant and thus prevent flicker.