Each also shows a declination diagram in its legend. In Maine, magnetic declination currently varies between 14-1/2 and 17 degrees west of true north, depending on your location.

S. C. N. Grant, Diagram for Determining the Parallaxes in Declination and Right Ascension of a Heavenly Body, and Its Application to the Prediction of Occultations, The Geographical Journal, Vol. 7, ...