A number of functions of a packhouse (Fig. 2) make it a useful model to study traceability systems. These include the following: (1) identifiable input units (bins) that hold groups of discrete but unidentified individual units (fruit); (2) use of a mass transit in-feed system, with considerable mechanical mixing, to move fruit to a sorting table at which point fruit are visually sorted and rejects manually removed; (3) fruit are then individually identified once they are on the grader,