Invoiced price minus the contracted price the customer was entitled to on the invoice date, per line. Over is overbilling that becomes credits and findings; under is margin given away. Both usually trace to a wrong tier or an undated price file.
A facility can be on contract and off price in both directions.
Underbilling is rarely re-invoiced. Correcting the tier stops it on every future line.
Invoiced price minus the contracted price the customer was entitled to on the invoice date, per line, with over and under kept separate.
Of 12,000 lines, 700 were invoiced above contract by $41,000 in total and 1,100 below by $63,000. Both are errors, with different consequences.
Netted. Over and under cancel and the report says pricing is accurate.