• A rare clockmaker’s sector, made circa 1800, engraved on the movable arm T. Jump.  Thomas Jump worked in Prescot, Lancashire.
   
• The sector is 17½ inches long and made of brass. The pinion sizing section of the scale is graduated 6, 7, 8, 10, 12, 14, 16, 18; the wheel sizing scale is graduated from 20 to 120 at one unit intervals. The rear of the sector is engraved 10, 12, 14, 16, 18, 20 in the pinion section and from 120 to 180 at one unit intervals in the wheel sizing area.
   
• The sector is a proportional gauge and was used principally for the rapid sizing of wheels and pinions. It can also be used for sizing spring barrels and their arbors. Detailed information on the construction and use of the sector is given in The Watch & Clock Makers’ Handbook Dictionary and Guide by F. J. Britten. The use of the sector was also described in the Horological Journal for January 1928, page 96.
   
• The sector, as a proportional measuring tool, was known in the seventeenth century. Thomas Jump is believed to be the first person to adapt the sector for use in clock and watch making. See Antiquarian Horology, December 1983 page 406.
  

Thomas Jump was a watchmaker, working in Prescot, Lancashire, when his wife gave birth to a son in 1785; he was still working in 1814. Later generations of the family were clockmakers in London, working for Vulliamy, before starting their own business.