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J. Picard, La Mesure de la Terre.
(Mémoires de l'Académie Royale des Sciences depuis 1666 jusqu'à 1699, tome VII, partie 1, pl. IV) Bibliothèque de l’Observatoire de Paris-Meudon (cl. n° 97/910)
The quadrant was used for precisely identifying and measuring angles, particularly in astronomy.
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