Production Report Repeats an Hour? Check Daylight-Saving Time
Local clock labels can repeat during a daylight-saving transition. Two records marked 01:30 may represent different instants. Preserve timezone or offset context before treating the second record as a duplicate.
Timezone behavior depends on location, date, and application scope.
What is happening?
Storage timestamps, gateway timezones, client display zones, and report boundaries can differ. A local day is not always 24 elapsed hours. Timestamp conversion must use the applicable rules for the instant rather than one fixed offset throughout the year.
Check these five things
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Identify stored timestamp type and timezone assumptions.
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Compare the original instant with its displayed local value.
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Inspect gateway, client, database, and report timezone settings.
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Test both repeated-hour and skipped-hour transitions offline.
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Define shift boundaries using the agreed operational calendar.
Worked example
In a location that repeats an hour when clocks move back, 01:30 at one UTC offset and 01:30 at another are different events. Deduplicating solely by the displayed hour and minute can delete valid production evidence.
Quick diagnostic reference
| Field | Purpose |
|---|---|
| Instant | Unambiguous event time |
| Offset or zone | Interpretation context |
| Shift identity | Operational grouping |
The mistake to avoid
Adding or subtracting a fixed hour from historical records can corrupt dates outside the transition. Correct the interpretation rules and preserve original timestamps.
How to verify the fix
Verify event counts, ordering, and shift totals across both seasonal transitions. Include a shift spanning the change and record how the report defines elapsed duration.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Inductive Automation: Date, time, timezone, and offsets. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.