Isogonic lines

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Related to Isogonic lines: aclinic line
(Magnetism) lines traced on the surface of the globe, or upon a chart, connecting places at which the deviation of the magnetic needle from the meridian or true north is the same.

See also: Isogonic

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
The upshot is that the isogonic lines showing magnetic variation on sectional charts shift more dramatically each time these updates are applied.
Many other presentations contributed accounts of little known or unknown artefacts, for example the MS chart of isogonic lines c.1585 by Luis Texeira, and often provided new interpretations of their production and contexts.
These lines are called "isogonic lines" unless it is indicating a zero variation, then it is called an "agonic line." A pilot uses these lines to correct the true course he drew on a chart for variation.