Manual validation of a single multiphase flow meter is a solved problem — pull the reference data, run the phase-split calculation, check it against tolerance. The trouble starts when that same process has to run across a fleet of meters, each operating at a different point on its calibration envelope, and each drifting at its own rate as water cut and gas volume fraction shift.
Spreadsheet models are built around a snapshot: fixed reference conditions and a fixed set of correction factors, evaluated at the moment someone opens the file. Multiphase production doesn't hold still. GVF and water cut move continuously, and a correction factor that was valid last month can be meaningfully wrong today — not because the math was wrong, but because the operating point it was built around has moved.
The failure mode usually isn't dramatic. It's a slow accumulation of small discrepancies across dozens of meters that nobody catches until an allocation dispute or a regulatory audit forces someone to reconcile the numbers by hand — at which point the spreadsheet's assumptions have to be reconstructed from memory and old emails.
Fleet-wide validation software solves this by treating each meter's uncertainty budget as a living calculation rather than a periodic snapshot — recalculating as field conditions change, and flagging when a meter has drifted far enough from its validated envelope to need attention.
That's the practical argument for software over spreadsheets: not that the underlying GUM mathematics changes, but that continuous, fleet-wide recalculation catches drift while it's still cheap to fix.