The machine is made up of several washing zones. The choice of the number of washing zones is determined by the number of items for washing and the time available. To achieve the best wash results the WD-B Green is designed with extra long washing zones of a full metre, and has the longest final rinse zone on the market at 1125 mm. This reduces water movement between the zones, otherwise known as carry over. Carry over involves the risk of dirty water from previous washing zones being carried into the next tank where there is cleaner water. It is particularly important to avoid this between the chemical wash and the final rinse tank.