Gyroscopes allow the orientation transfer from a reference line to another line without the need for a connecting geodetic network. They are used routinely for orientation control of networks in tunnel construction projects. This is currently the only way to stabilize the accuracy in slender tunneling networks and is indispensable in view of today’s requirements for the excavation and breakthrough accuracy. In order to archive a reliable assessment of correctness, the measuring method has to be planned in such a way that systematic influences in the determination of an underground directional angle are minimized. For this purpose, the difference principle is used for an azimuth determination both in terms of time as well as in space, and all required corrections and reductions must be regarded correctly to obtain the directional angle of interest with measurement uncertainty ≤1 mgon.