[crote]

You can even subscribe to services which do this for you! There are a few companies with large-scale networks of fixed receivers, and you can get the observed offset from a node near you via the internet, usually via "NTRIP".

Getting correction data from a node a few dozen kilometers away isn't quite as good as having your own fixed base station a stone's throw away, but it's way more convenient and for a lot of applications plenty accurate.