Rare Clockmaker's Sector or Proportional Gauge, circa 1800.
Brass, the short bevelled pinion section engraved 6 to 18, with the long wheel section arm engraved 20 to 120 and divided into tens, with no engraving on the rear or the locking slide. 16 1/2 inches (42 cm) in length.
Thomas Jump, working in Prescot, is thought to have been the first to adapt this form of proportional gauge for use in clockmaking. See the article 'The Jumps and their Sectors' by Vaudrey Mercer in Antiquarian Horology, December 1983, pages 406-11. See also Britten's Handbook... for a full description of its use.
NB: I believe this to be an unusually early example, and is the only Jump sector known to me that is signed 'Thos Jump' rather that 'T Jump'
Good clean, unpolished condition.
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