Determining height displacements of Earth's surface is one of the most demanding geodetic tasks due to the constant influence of different natural processes. The result of such action is a change in the elevation of permanently stabilized points. In the Republic of Croatia, the height systems are based on tide-gauge measurements that determine the mean sea levels as reference points. Mareographs, devices for measuring sea level, play a key role in this process. The aim of this thesis is to investigate the height displacements at the Bakar tide-gauge station, with special emphasis on the role of tide-gauges in height systems. The height changes over a certain time were analyzed. The function, significance and way of working of the tide-gauge are explained in detail, and an insight into the existing condition of the tide gauge station and the surrounding high benchmarks is provided. Height systems in Croatia since the precise levelling network of the Austro-Hungarian Monarchy (APN) have been reviewed, with an emphasis on the II. levelling network of high accuracy (IINVT). Geodetic surveying and the application of the precise geometric leveling method are described. The computational processing of the original data and adjustment in the JAG3D software are also presented. Height differences between identical benchmarks in certain epochs of measurement were analyzed. At the end, a comparison of the final heights of the benchmarks is given. All results and detailed calculation procedure are attached within this work.