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"Used with indistinct or invisible targets and to define sectors." — Moss, 1914

Finger system

"Used with indistinct or invisible targets and to define sectors." — Moss, 1914

"The sextant, an instrument of reflection used by navigators for measuring the altitudes of heavenly bodies."—Finley, 1917

Sextant

"The sextant, an instrument of reflection used by navigators for measuring the altitudes of heavenly…