Measurement of declination at South Georgia 1700–1984
Declination, or the difference between true and magnetic north, is one of the earliest parameters to have been measured systematically over the earth's surface. Values are available for South Georgia and the surrounding area from 1700 to the present. Observations were made from ship by Edmond Halley in 1700, by James Cook in 1775 and thereafter more frequently. Land-based observations were made during the First Polar Year in 1882–3, more recently by the British Antarctic Survey 1975–82. Declination has diminished from 23°E in 1700 to about 9°W in 1980, approximately 0.1° per annum. The modern observations suggest that the rate of change has slowed in recent years.