methods and apparatus , including computer program products , implementing and using techniques for managing data items in an inventory management system . a set of data items representing stock items is maintained in an inventory , wherein at least one stock item is described by two or more values . each value being expressed in different units of measurement . a change request for a change of the values for the stock item that is described in the two or more different units of measurement is received . the two or more values for the stock item that is described in two or more different units of measurement are updated .