German federal authorities buy IT under the EVB-IT, standard contract terms published by the Federal Interior Ministry. They are binding for federal authorities. The EVB-IT system contract provides a Funktionsprüfung, a function test, before acceptance. Unless agreed otherwise, it lasts 30 days. Defects fall into three named classes. A betriebsverhindernder Mangel prevents operation. A betriebsbehindernder Mangel hinders operation. A leichter Mangel is a minor defect. Requests for changes are handled under their own clause.