an instrument with a graduated arc of 60o and a sighting mechanism, used for measuring the angular distance between objects and especially for taking altitudes in navigation and surveying
The sextant was used to navigate ships through charted and uncharted waters from the 1700's onwards. It measures the angle a heavenly body makes with the visible horizon, and derives its name from the arc at the bottom which is one sixth of a circle. The principles of a sextant are easy to master but its use requires skill and experience.
why does Livingstones use the sextant metaphor?
taking reference from two or more points of view (listening & understanding)
establishing & verifying factual data (reporting & recording)
navigating a safe course (planning & implementing)