TL;DRA dated table of published values — a fuel index, say — that a rate card references instead of hardcoding.
A fuel surcharge that tracks a weekly diesel index needs the index, by date, somewhere. A rate index holds those values; the rate line references it and rating looks up the value for the shipment date.
An index can carry carrier-specific branches: a default table plus alternative tables for listed carriers. A missing date on the chosen table does not fall back to another.
Where it happens in Sonic
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See it on your contracts
A walkthrough on the agreements and files you actually bill from — not a slide deck.