ECO.2:4.1 - Establish the changed exchange

Compare like terms: unit, specification, quantity, time, location, payment and access. Determine which part changed and which obligations already fix the price for the current work. Include a consequential service or supply condition even when the quoted money amount stays constant.

Ask whether the change applies at the margin of the contemplated action. A cheaper bulk offer may require more storage than is available. An average historic price can be irrelevant to the next attainable unit. ECO.1 supplies a missing interpretation.