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