 It may exist also when a MES system is being used when no back flushing is needed.The reason for this is that any error in transmitting and/or interpreting the data being sent by the MES system to the ERP system is consigned and needs to be worked out.When using back flushing, any scrap, material usage variance (using more or less than specified in the BOM) or substitution must be reported separately in order to maintain acceptable inventory accuracy.