A small rounding choice can accumulate
If a production spreadsheet converts frame positions into time, preserve the source rate as a rational value. A display reading close to thirty frames per second is not sufficient evidence that thirty is the correct divisor. This matters for an owned recording's edit notes, caption reconforming or event references.
Consider an invented position 108000 frame intervals from the chosen origin. Dividing by 30 gives 3600 seconds. At 30000/1001 intervals per second, the same count represents 3603.6 seconds. The 3.6-second difference comes from the arithmetic assumption; it does not establish that the camera drifted.
Keep the origin convention explicit as well. A frame labelled zero and the first displayed frame labelled one can introduce a separate one-frame discrepancy. Write which convention the worksheet uses before comparing it with an editor's time display.
Keep the calculation traceable
Store the original rational rate and frame count, then round only the human-readable result. Label elapsed seconds separately from a formatted timecode string. If the source is variable rate, do not force frame count divided by one nominal rate to stand in for the actual presentation timeline.
FFprobe's stream and frame reports can support the inspection, but record which fields and intervals were used. If the source rate is unknown, keep that uncertainty instead of choosing a convenient integer. Verify the resulting reference against a recognisable event in the delivered media.
When fixing an existing worksheet, recalculate a beginning, middle and late reference. A nearly correct opening value can conceal an increasing arithmetic error. Retain the old calculation long enough to explain which assumption changed and which downstream references need updating.
Questions answered
Does a rounded thirty-fps display prove an exact rate of 30?
No. Preserve the underlying rate and source timing information.
Does a late mismatch always mean capture-clock drift?
No. First rule out accumulated error in the conversion arithmetic.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.