that measures how far the arbor has been turned, compared to the barrel. Unusual forms of mainspring A mainspring is usually a coiled metal spring, however there are exceptions: The wagon spring clock: During a brief time in American clockmaking history, coilable spring steel was not available in the United States, and inventive clockmakers built clocks powered by a stack of leaf springs, similar to what has traditionally served as a suspension spring for wagons. Other spring types are conceivable and have been used occasionally on experimental timepieces. Occasionally one finds an odd clock with a spring made of material other than metal, such as synthetic elastic materials. Notes References G.A. Berner 4-language Glossary, 1988 re-edition, courtesy FH, Federation of the Swiss Watch Industry, Bienne, Switzerland. External links Federation of the Swiss Watch Industry Dictionary Timekeeping components Springs (mechanical) Horology