To improve a surgical referencing unit for a surgical navigation system, with which a spatial position and/or orientation of the referencing unit is determinable, the referencing unit comprising a base body and at least one marker element arranged on the base body, and the spatial position of the marker element being determinable by the navigation system, so that the handling thereof is simplified and possible errors are eliminated during use thereof, it is proposed that the at least one marker element be movably mounted on the base body, that the referencing unit comprise a first interface device which is configured for engagement with a second interface device provided on a surgical instrument or an implant in a connected position, and that the at least one marker element be movable into a predefined marker element position in dependence upon the interacting first and second interface devices.An improved surgical instrument and an improved surgical navigation system are also proposed.
