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Compass on Gimbals
Public DomainCompass on Gimbals
Gimbals are pivoted rings that allow a compass or other object to remain stationary while the supporting base moves in any dimension.   Supposedly the first use of gimbals was in a Greek curiosity: an octahedral inkpot with a hole in each of its eight sides.   The inkwell was held upright inside on gimbals, whichever way up the inkpot was turned.