Is there a tolerance on yield to account for any concreting materials left in the mixer drum after discharge? If not, who is responsible for the underyield? Allowable variations in air content and batch weights can also cause yield to vary. But a cubic yard still has to contain no less than 27 cubic feet. This article also shows how testing procedures can affect yield. There is an analysis of what affects yield as well. [keywords: yield, underyield]