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The Encyclopedia of Horology

Glossary · Regulation

Regulator (index)

A sliding lever that effectively lengthens or shortens the active portion of the hairspring to adjust rate.

Explanation

Moving the index toward 'F' (fast) shortens the spring's active length and speeds the watch; toward 'S' (slow) lengthens it. Fine regulation on higher-grade watches instead uses a swan-neck or micrometric screw for finer control without disturbing beat.