Only in the middle of the 18th century, after the marine chronometer was invented and the spatial distribution of magnetic declination was known, could the Mercator projection be fully adopted by navigators.
Først omkring midten af det 18. århundrede, hvor skibsuret var opfundet, og hvor fordelingen af den magnetiske deklination på Jordens overflade var kendt, kunne Mercatorprojektionen anvendes fuldt ud af navigatører.