The market is full of geodesic equipment manufacturers, each with various claims as to the accuracy of their products. In the scope of this thesis, we have measured the addition constant of three GMP 111 mini prisms, and examined how accurate the manufacturer's claims are. The thesis also presents electronic distance measurers and reflectors. Various different errors, which affected the quality of the measurements, are detailed in the thesis. Its core consists of the analysis of the addition constant. The measurements were done both indoors and outdoors. We made three series of measurements for each prism over three different distances; those were the source of my results. These were then compared with the manufacturer's claims and were analysed in the conclusion.