## 4 Results  
The analysis evaluated the speed of the benchmarks' height change corresponding to the geological structure of the Szczecin area, as shown in Figure 5. The analysis was conducted using the formula:  
* RMSE average variation in excess, \[m_{\pi\lambda hi}=\pm 2\sqrt{2}m_{\Delta hi}\] (1) where: \[m_{\Delta hi}\text{--RMSE of the $i$-th overrun;}\] \[m_{\pi\lambda hi}\text{--RMSE $i$-th difference in elevation.}\]
* The speed at which the altitude changes, \[V_{n,n+1}=\frac{\Delta H_{n,n+1}}{T_{n+1}-T_{n}}\] (2) \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Position**} & \multirow{2}{*}{**Height (Precise**} & \multicolumn{2}{c}{**Height (GNSS)**} \\  & & **Measurements—November 2020 Aligned** & **Difference of Height** \\  & & **to ASG EUPOS Reference Stations** & \\ \hline
1 & 17.4883 & 17.488 & 0.3 \\
2 & 4.5825 & 4.582 & 0.5 \\
3 & 13.0060 & 13.006 & 0 \\
4 & 5.1784 & 5.177 & 1.4 \\ \hline \end{tabular}
\end{table} 
Table 2: The height of benchmarks in stable positions and in position near the EcoGenerator, from precise levelling and GNSS-GPS measurements. Figure 6: Location of measurement sites in relation to the nearest reference stations: Choszczno, Goleniów, and Kamién Pomorski. where:  
\(V_{n,n+1}\)--Speed of changes in altitude of benchmarks in the period between \(n\) and \(n+1\); \(\Delta H_{n,n+1}\)--The difference in the height of benchmarks between epochs;  
\(T_{n}\)--Year of the measurement epoch \(n\);  
\(T_{n+1}\)--Year of the measurement epoch \(n+1\). - RMSE of speed of altitude changes,  
\[m_{V_{n,n+1}}=\pm\sqrt{\frac{2m_{0}^{2}R_{i}}{\left(T_{n+1}-T_{n}\right)^{2}}} \tag{3}\]  
where:  
\(m_{0}\)--RMSE of altitude change over a distance of \(1\) km;  
\(m_{V_{n,n+1}}\)--RMSE of speed of altitude changes;  
\(R_{i}\)--Distance of the \(i\)-th benchmark to the reference benchmark;  
\(T_{n}\)--Period of the measurement epoch \(n\);  
\(T_{n+1}\)--period of the measurement epoch \(n+1\). Values of velocities benchmarks height are from \(-0.13\) mm/year to \(-0.18\) mm/year. Benchmark numbered 14 in the Figure 3 show a significant value (\(-2.52\) mm/year). This is the result of increased ground weight in the area of the extended harbor quay. Lower velocities of changes in the altitude of benchmarks can be noticed in their RMSE limits [11] (Figure 3). The velocity values of changes in the height of benchmarks from the area of Miedzy-odrze are higher in comparison with those in other parts of the city. This underlines the unstable geological structure of this area. The software Trimble Business Centre [12] was used to process baselines between the observation stations and the nearest reference stations, as shown in Figure 6.  
The height of benchmarks obtained from the precise levelling and GNSS satellite measurements are summarized in Table 2. The height of benchmarks located in the immediate vicinity of the measurement positions, obtained using precise levelling, were converted to the EVRF 2007 system [13,14]. They are compared with heights from the GNSS measurements. The stability of the benchmarks was confirmed in the case of stable sites, while in the area of the EcoGenerator site displacements of 1.4 mm per month were visible. Next, GNSS measurement, performed in May 2021, allowed us to verify the results. Table 3 shows the coordinates aligned to ASG-EUPOS stations from measurements which lasted 6 h.  
The 6 h measurement showed the same accuracy of height alignment as the 3 h measurement (Table 4).