A 4% Geometric Distance to the Galaxy NGC4258 from Orbital Motions in a Nuclear Gas Disk by J. R. Herrnstein and others (1999)

Primary research, Nature 400, 539–541, DOI doi.org/10.1038/22972. The preprint title includes the 4% qualification. The observed water-maser proper motions and accelerations in NGC 4258 supply an orbital distance anchor independent of stellar standard candles.