Editing Arc measurement (section)

==Extensions==
[[File:Clarke figure of the Earth 1860 (cropped).jpg|thumb|upright=2|right|Arc measurements used in Clarke's Figure of the Earth, 1858]]
Additional arc measurements, at different latitudinal bands (each delimited by a new pair of standpoint and forepoint), serve to [[Earth ellipsoid#Determination|determine Earth's flattening]].
[[Friedrich Bessel|Bessel]] compiled several [[meridian arc]]s, to compute the famous [[Bessel ellipsoid]] (1841).
[[Alexander Ross Clarke#Figure of the Earth, 1858|Clarke]] (1858) combined most of the arc measurements then available to define a new [[reference ellipsoid]].<ref>{{cite EB1911
| ref = {{harvid|Britannica|1911a}}
| last  = Clarke
| first = Alexander Ross
| last2  = Helmert
| first2 = Friedrich Robert
| author2-link  = Friedrich Robert Helmert 
| wstitle = Earth, Figure of the
| volume = 8
| pages  = 801–814
}}</ref>