Canon EOS 6D Instruction Manual page 222

3 Setting the Time Code
Drop Frame
If the frame rate setting is 6 (29.97 fps) or 8 (59.94 fps), the time
code's frame count causes a discrepancy between the actual time and
time code. This discrepancy can be corrected automatically. This
correction function is called drop frame.
[Enable] : The discrepancy is corrected automatically by skipping
time code numbers.
[Disable] : The discrepancy is not corrected.
If the frame rate is 4 (23.976 fps) or if the [Video system] is [PAL] (with
7/5 set), the drop frame will not work ([Drop frame] will not be
displayed).
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