## Results
In the case of Aden, one segment, the first of five, shifted down first, then up again 150 mm, for a misinterpretation of the published information about the tide gauges [21]. Over seven years, PSMSL has provided three different versions of the composite record of Aden, resulting in a strongly variable sea level rate of rise and acceleration. The historical data from 1879 to 1893 were first shifted down 150 mm, thus producing a much larger slope, but also a negative acceleration. Then, these data were shifted up again 150 mm, to produce a smaller slope, but a positive acceleration. The PSMSL pattern (\(n-2\)) of 2007 [23; 24] suggested a slope for Aden of \(+1.21\) mm/yr with data from 1880 to 1969. The PSMSL pattern (\(n-1\)), valid up to about 2013, with a data range March 1879 to December 2010, suggested a slope of \(+3.067\pm 0.222\) mm/yr, and acceleration \(-0.0237\pm 0.0099\) mm/yr\({}^{2}\)[21]. The PSMSL pattern (\(n\)) was then corrected only because of the large negative acceleration. As written in [25], \"this resolves the anomalous negative acceleration value derived from the previous uncorrected data\". With dates ranging from March 1879 to December 2010, the slope is \(+1.330\pm 0.193\) mm/yr and the acceleration is \(+0.0241\pm 0.0085\) mm/yr\({}^{2}\), a similar module but opposite sign. The rates of rise and accelerations have dramatically changed three times over a decade. In the case of Aden, the alignment of the first segment in particular, but also the alignment of the last segment, appears questionable. As the network of benchmarks was compromised at the time the new tide gauge was set up, after a gap of 40 years from the prior measurements [21; 26], the alignment of the new tide gauge was quite complicated. The Technical Survey [26] provided a clear description of the different tide gauges around Aden and the issues with the benchmarks: \"The Great Triangulation Survey of India (GTS) provided various benchmarks around Tawahi Port of  
Figure 3: Aden MSL results. (**a**) Version (\(n-1\)), data sources are 795 months from the National Oceanic and Atmospheric Administration (NOAA). (**b**) Version (\(n\)), data source 815 months from Permanent Service for Mean Sea Level (PSMSL). Mumbai MSL results. (**c**) Data source 1465 months from PSMSL. Karachi MSL results. (**d**) Data source 673 months from PSMSL. Frematle MSL results. (**e**) Data source 1331 months from PSMSL. Aden\". However, \"The primary benchmark at Fairway House/Post Office House next to Post Office Pier no longer exists and the other remaining vertical benchmark is at the North-East corner of the Port Engineers Office (PEO). There is another benchmark at the Pilots Pier tide gauge hut, situated on the lower wall by the steps next to the tide staff. Both benchmarks are in poor condition and need urgent repairs or replacing\". [26] concluded, \"Re-establishing a new network of benchmarks should be a priority\". Even though the Great Triangulation Survey of India (GTS) provided various benchmarks around Aden to align with the tide gauges of the time, nevertheless PSMSL made a mistake of 150 mm, misaligning the first segment with the others. Then, as the benchmarks were lost at the time the new tide gauge was set up, it is unclear how the alignment of the new tide gauge could have been performed with accuracy. In the case of Aden, but also Mumbai and Karachi, the last segments, from the new, recently established tide gauges, which were started almost simultaneously in the three locations as part of a common international monitoring project, are very likely all misaligned with the prior segments from the historical tide gauges after substantial gaps in the measurements [2; 3; 21]. The procedure outlined in the Method section was applied to the tide gauge records of Aden, Mumbai, and Karachi. The different segments were detected first. Then, the breakpoint alignment was attempted. Finally, consistency with the Fremantle tide gauge record was tested.