Before the satellite era, the best data we have about sea level comes from tide gauges. They give local sea level, which is the difference between the height of the sea surface and the height of the land (it can move up and down too). It is possible — but very complicated — to combine data from tide gauges around the world in order to estimate how global mean sea level (GMSL) has changed over the past century-and-a-half or so.
The two best-known such estimates come from two different teams of researchers; one from Church & White (which I’ll refer to as “cw”), the other from Jevrejeva et al. (which I’ll refer to as “jev”). Let’s compare them. Here they are: