Measuring sea level
I’ve always wondered how sea level is measured so accurately. Global sea level changes are measured to high accuracy. The global yearly sea rise averaged over many years is measured to a fraction of a mm. There are two ways sea level is measured. The old system uses tidal gauges, and satellites were launched in 1992 (TOPEX/Poseidon) and 2005 (Jason-1).
Here’s a page explaining how the tidal gauges work: Univ. of Colorado. Ah, stilling well!
