
Theodolite used for the Principal Triangulation of Great Britain
1791
1791
1801
1794
1798
1797
1800
1795
1791
1800
1787
1790
1796
1794
1800
1800
1800
1792
1795
1800
1790
1795
1795
1790
1792
1792
1790
2000-100 BCE
1799
1788
circa 1801
mid-1800s
1705-1737
1797
1800
1788
1791
1790-1794
1799
1795
1787
1800
1797
1801
4000-2001 BCE
1799
1790
1642-1649 (original); 1883 (model)
1936
1990-95
1610; 1923