What is clock drift?¶

Clock drift is the gradual movement of a device clock away from a reliable time reference. A clock that gains or loses a little time on each cycle can become seconds or minutes wrong, even though nobody changed it.

Drift can distort a sequence progressively¶

Hardware tolerances, temperature, power conditions and virtualisation can affect timekeeping. Network time services normally compare the clock with reference servers and correct the difference, but synchronisation may be intermittent, blocked or faulty.

The resulting error need not remain constant. An event might be 20 seconds early at the start of a period and 90 seconds early later. Applying one correction to every timestamp could therefore create a false sequence.

Reconstruct the clock's behaviour from records¶

Time-service logs can record reference servers, measured offsets, corrections and failures. Restarts, manual changes and stable external events may provide further comparison points. A current clock check is useful context, but it does not establish the historical offset.

Plotting supported comparisons across the relevant period can show whether the error was stable, increasing or reset by synchronisation. Where the records cannot measure drift reliably, preserve the recorded values and express the resulting timing uncertainty instead of inventing a correction.