Short-run offset crossover point.

Offset spends before the first good sheet: plates, makeready, the waste run up to color. Spread across enough copies that spending disappears, so offset's cost per copy falls as the quantity climbs while digital's stays close to flat, and the crossover point is where the two lines meet. Digital's side of the comparison is published and per-unit, with KDP putting the printing cost of a 333-page black-ink paperback at $5.00 whatever the volume (KDP paperback royalty). Offset's side is a quote, and a quote carries assumptions that move the crossover by hundreds of copies: paper price on the day, how cleanly the page count fills its signatures, sheetfed or web, and whether the printer is filling a slot they wanted filled. The assumption that moves it most is never in the quote at all, which is what the unsold copies are worth. A crossover computed on copies printed rather than copies sold is arithmetic about a warehouse, and the pulping bill arrives long after the decision it justified.