Why your two reports disagree

When two reports of the same thing disagree, the instinct is to look for a broken query. Occasionally that is what it is. Far more often the reports are both working exactly as built, and what differs is the question each one quietly decided to answer.

The usual suspects

Timing is first. One report counts a shipment when it leaves, the other when it is invoiced. Across a month end, those are different months. Second is inclusion: does an intercompany transfer count as revenue? Does a credit note reduce this month or the one it corrects? Third is late-arriving data — a report run on Monday and re-run on Thursday will not match if anything backdated arrived in between, and both runs were correct when they happened.

None of these are errors. Each was a decision someone made for a good local reason and nobody wrote down.

Reconcile one month, completely

The temptation is to compare twelve months and look for a pattern. Resist it. Take one closed month and account for every unit of the difference until nothing is left over. It is slower for the first day and much faster overall, because a cause you find in January explains the other eleven months for free.

Stop when the gap is fully explained, not when it is small. An unexplained remainder of two percent is not a rounding difference; it is a cause you have not found yet, and it will grow.

Then write the rules down

The output of a reconciliation is not a corrected number. It is a short document saying what each report counts, which differences are deliberate, and which were bugs now fixed. Deliberate differences are fine — two audiences legitimately need different views. What is not fine is nobody being able to say which is which.

Once that page exists, the monthly meeting stops relitigating arithmetic. That, rather than any dashboard, is the deliverable.