What I found
The metric was impossible until the source was clean. Overlapping payroll exports and amended punches survived as separate rows: about 1,180 duplicated employee-days, 6,720 duplicated hours, and 1,080 copies that did not even agree with each other. Any average built on that was going to be wrong in a way nobody could trace.
What I built
A load that treats a day as one thing. It replaces a day whole rather than mixing rows from two files, records where every row came from, writes the tie-break rule down, and logs the conflicts it cannot resolve instead of quietly dropping them.
How it works
Click through the four fixes and watch the duplicate count fall to zero while the exceptions tab fills.
128,000 punch rows · 310 employees · 11 months of data
- One version of a day
- Source and period tags
- Written tie-break rule
- Retry and log
The problem
Overlapping payroll exports plus amended punches surviving as separate rows
The tie-break rule is the quiet part that matters: the latest pull wins, because it carries the corrected punch. It is written down, so the load makes the same decision every time and anyone can check it.
Impact
- Duplicated employee-days went from about 1,180 to 0.
- About 2,040 conflicts, roughly 9,350 hours, are logged to an exceptions tab instead of silently distorting the average.
- The hours-per-unit metric could finally exist, because its input could be reconciled.
The transferable lesson
Fix the source before the metric. A number built on data you cannot reconcile will be wrong in a way that surfaces months later, in a meeting, when it is hardest to explain. A written tie-break rule and an exceptions log are cheap insurance against that.