Troughton's dividing engine, 1778.
© Science Museum / Science & Society Picture Library
Completed by John Troughton (c 1739-1807), this is similar to the first succesful dividing engine which was completed in about 1775 by Jese Ramsden (1735-1800). Until the 1770s, scales on scientific instruments had been marked out by skilled craftsmen in a proces called 'dividing', this was partly mechanized from the 1770s when dividing engines were introduced. Originally used on small instruments, by the 1850s they were used to graduate scales on large astronomical telescopes, making hand-dividing obsolete.