Alteration of timecode to match the framerate of NTSC video to a time of day clock. NTSC video actually runs at 29.97 frames per second (30/1.001). To keep the timecode on an NTSC videotape synchronous with a time of day clock, it needs to make up 1 in 1001 frames. It does this by changing the count by two frames on nine out of every ten minutes. So the frame following 10:35:59:29 would be numbered as 10:36:00:02. 30 frame HD formats are often run at 29.97 to allow conversion and synchronization to NTSC video. These formats support Drop-Frame timecode. Note that there is no drop frame format for native 24-frame video formats. Also see Non-Drop-Frame, Timecode.