Here’s a novel approach. Beenstock et al wondered if tide gauges were placed in any old spot around the world or were biased toward area where sea-level did more rising. They compared the location of tide gauges in the year 2000 to sea level rises and falls as measured by satellite altimetry. It turns out the placement seems to be independent (meaning anywhere). This is pretty important because the infernally tough thing about measuring sea levels is whether the land is subsiding or rising at the same time, and how to correct for that. If tide gauges are spread evenly (or quasi-randomly), it means we could average the lot instead of trying to correct and reconstruct each one individually. So that’s what they did – average (they did not reconstruct).
The consensus estimate is that sea-levels are rising by 2mm a year (and 3mm lately, with adjusted satellite data). Beenstock et al used 1,000 tide gauges and found global sea level rise was more like 1mm a year (very similar to the rise Nils Axel Morner found on that stable spot in Denmark). The conclusion is that sea level is rising slowly at 1mm a year, and that it hasn’t changed, and that local sea level rises and falls are very common, and that correcting for them is risky.