The magnetic charts of the United States for Epoch 1975

Circular 810
By: , and 



Approximately 24,000 measurements taken from 1900 to 1974 were analyzed by least-squares methods to produce a series of five magnetic charts of the United States for 1975. A feature of the analysis, differing from techniques used for previous editions of the national chart, is that analytic models define the regional magnetic field and are used to contour the magnetic charts. An overall rms (root mean square) fit of less than 235 nT was obtained for the horizontal and vertical intensities; for the chart of magnetic declination, the rms deviation was on the order of 0.5 degrees. The models of annual change, derived from data at repeat stations and observatories operated by the U.S. Geological Survey, yielded an rms deviation of approximately 6 nT/yr in the force components and 0.7 min/yr in magnetic declination.
Publication type Report
Publication Subtype USGS Numbered Series
Title The magnetic charts of the United States for Epoch 1975
Series title Circular
Series number 810
DOI 10.3133/cir810
Edition -
Year Published 1979
Language ENGLISH
Publisher Branch of Distribution, U.S. Geological Survey,
Description iii, 15 p. :ill., maps ;26 cm.
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