The “four-eye-principle” is an essential component of quality assurance in building projects. The consulting engineers Dipl.-Ing. Peter Bock, Dipl.-Ing. Dieter Lippold and Dipl.-Ing. Roland Wetzel acquired the status as proof engineers in 1988. Since then, the have been supervising diverse projects including highly complex constructions. Besides their sovereign proof activities, they are also working on behalf of insurances and clients, expecially abroad, where proof engineers in our sense do not exist.