Pricing mode tells the ring how the bid maps to money:
Per cwt — bid is dollars per 100 lbs, multiplied by the lot's aggregate weight.
Per head — bid is dollars per animal, multiplied by the head count.
Lump sum — bid is the total price for the whole lot, no multiplication.
The reserve price and the sale's unit price are always quoted in the same unit as the pricing mode. A per-cwt lot's reserve is dollars per cwt, not a total — don't compare them across modes.
Technical section
Data model, API, and internals — visible to developers.