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isogonic line[′ī·sə¦gän·ik ‚līn]
Any of the lines on a chart or map showing the same direction of the wind vector.
Any of the lines on a chart or map connecting points of equal magnetic variation.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved