GNSS-instrumente (angl. Global Navigation Satellite System) uvrščamo med standardno terensko geodetsko mersko opremo (poleg elektronskih tahimetrov in nivelirjev), ki jo lahko uporabljamo za vzpostavitevgeodetskih mrež in za detajlno izmero. Podobno kot pri drugih geodetskih instrumentih moramo tudi pri GNSS-instrumentih pred izmero ovrednotiti parametre kakovosti instrumentarija oziroma metodeizmere, ki jih pridobimo s postopki laboratorijske kalibracije in/ali s terenskim preizkušanjem. Tako pridobimo podatek o ustreznosti navedenih tehničnih značilnostih proizvajalca in ovrednotimo primernost uporabe GNSS-instrumentov za konkretne potrebe.Mednarodna organizacija za standarde ISO (angl. International Organization of Standardization) je v okviru tehnične skupine 172 in podskupine 6 (ISO/ TC 172/SC 6) v letu 2007 predstavila postopkepreizkušanja GNSS-merskega instrumentarija za določanje položaja v realnem času, ki temeljijo na oceni kakovosti delovanja strojne in programske opreme posameznega instrumenta. Preizkus lahko opravimo kjerkoli na terenu, kjer so zagotovljeni primerni pogoji za izvedbo GNSS-opazovanj predvsem s stališča čim manjših vplivov na opazovanja zizvorom v okolici. Preizkus tudi ne zahteva dodatnega programskega orodja za obdelavo podatkov meritev, saj je statistično vrednotenje rezultatov opazovanj dokaj enostavno. V prispevku opisujemo teoretične podlage preizkusa GNSS-instrumentov po navodilih standardaISO 17123-8, ki jih uporabimo za praktični preizkus GNSS-instrumenta. ; GNSS-instruments (Global Navigation Satellite System) are the standard field surveying equipment (in addition to tachymeter and levels) for geodetic network establishment and detail surveying. As inthe case of other geodetic instruments, it is essential to pre-analyse GNSS-receiver quality parameters, obtained from laboratory calibration and/or field testing of the specific nstrument and/or measuring method. Thus, the relevance of the results, as indicated by manufacturer, is obtained that may explain the suitability of a specific GNSS-instrument for field measurements. In 2007, the International Organization of Standardization (ISO), Technical Committee 172, Subcommittee 6 (ISO/TC 172/ SC6), presented a comprehensive GNSS field testing procedures for real time measurements, based on statistical evaluation and verification of themanufacturer’s hardware and firmware. The test can be performed anywhere on the field assuming that the test area includes minimal potential influences to GNSS measurements. At the same time, a test does not require any additional processing software, because the test data evaluation is based on elementary statistics. This paper presents the theoretical basis of GNSS instrument testing in accordance with the ISO 17123-8 guidelines and further examination of specific measurements on the selected site.