TL;DRPrice bands by quantity — graduated charges each band its own rate; volume charges everything at the band the total lands in.
Graduated: the first 100 units at one price, the next 400 at a lower one, and so on, so a single invoice line can be split across tiers. Volume: the total quantity decides one rate for all of it.
Both models exist for usage and seats. For a seat product with a proration factor, the factor is applied after seats are split across tiers so a five-day stub bills five days of each band, not a full quarter.
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.