Various studies at the Geodetic Institute of TU Dresden show that a height difference determined by GNSS and based on swapped antennas can provide accuracies in the millimeter range. Extensive investigations into this have been carried out on data from a GNSS measurement campaign at Schräh dam in Innerthal (Switzerland). The focus of this investigations is on the repeatability that can be achieved, when the height differences using GNSS are calculated as antenna-exchange mean-values. Height differences of up to 70 m are considered in this study and the length of the baselines is up to 1 200 m. Furthermore, obser-vation periods of eight to 24 hours have been evaluated. Most of the GNSS surveying points were set up with tripods for several days. In order to detect tripod movements, the height has been closely monitored by leveling. The results prove that the height differences, determined with antenna swap, show a higher repeatability than height differences without antenna swap. In the Wägitalersee area, 12-hour solutions have proven to be optimal for high-precision measurements. Standard deviations of 1 mm can be achieved, even if the signal shading is highly increased. Thus, in selected areas, GNSS has the potential to thin out or even replace measurements using precision leveling. Another advantage of antenna-exchange mean-values is that antenna calibration values can be neglected. Based on these results, further investigations are planned. On the one hand, other fields of application are to be explored; on the other hand, it is important to evaluate the accuracies for the detection of deformations over several measurement epochs.