Keep derived estimates and source records in separate fields

Symptom

Cost was computed as foreign price x rate x coefficient. Compared against the actual payment record, it was off by 16% (estimate 115,470 vs actual 99,000).

Cause

The coefficient is an average and the rate is from a different moment. The estimate isn't wrong in itself — but a source record existed and was going unused. The payment confirmation email had the real figure.

Fix

• Create a dedicated field for measured values. When present, it always wins
• ★ An estimate is a stand-in for a missing source, not an equal. Mixed into one field, you can no longer tell which you have
• Flag records judged from estimates alone. 16% is enough to flip profit into loss

★★ The longer the estimation pipeline, the more quietly a single bad input skews it. This one had three inputs (price, rate, coefficient) — and the currency itself had been wrong at one point.

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