This part of ISO17123 specifies a field procedure for the verification that a given Global Navigation Systems (GNSS) -based system and measurement procedure meets a required measurement uncertainty at the location and time of interest. The field procedure uses three-dimensional coordinates which are compared to reference coordinates. It is designed to be applicable to the technically versatile GNSS systems on the market and can be used for any kind of GNSS based coordinate determination application, not only geodetic. It is independent of the technology used in the GNSS measuring instrument, the satellite data streams, and any correction data used. The procedure is applicable to GNSS instruments under use conditions in the field in such a way, that the main parameters affecting the determination of coordinates are included in the result of the test. Several delimination criteria defined by the document allow a versatile applicability so the verification procedure can be performed regurarly in the fielw with limited economic impact.