Change database will offer you a file dialog where you can select another database file ( *.odb). It is possible to have many different substance databases. The default database delivered with GREAT-ER (substance.odb) should only be modified/extended if the new values can be trusted (literature/laboratory reference). If you need to work with a large amount of substances, the substance database concept enables you to store substances in different databases by classes. This increases the transparancy of data storage and speeds up data retrieval.