evertz 5010 SIE Instruction Manual page 18

Model 5010 Time Code Generator / Reader Manual
DROP FRAME: In NTSC systems, where the frame rate is 29.97002618
frames per second, the drop frame mode permits time of day
indexing of the frame numbers by dropping certain frame
numbers. Specifically, frames 0, and 1 at the beginning of each
minute except minutes 0, 10, 20, 30, 40 & 50 are omitted to
compensate for an approximate timing error of 108 frames
(3 seconds 18 frames) per hour. A flag bit is set in the time
code to signal when the drop frame mode is in effect.
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