To effective create maps of their route, Captains Lewis and Clark needed numerous instruments. While at White Catfish Camp, just south of today’s Omaha metro area, Lewis entered in his journal most of the equipment he and Clark used to make celestial observations. This included spirit and telescopic levels, compasses, an octant, rods and chains, telescopes, artificial horizons, drafting instruments, a simple version of a measuring tape, and a clock or chronometer.
They also used books and tables which provided information about locations of the sun, moon, and planets for use in determining the geographic locations after sighting the celestial objects.
The chronometer, possibly similar to this one, was the only form of accurately telling the time upon which many other calculations were based.
William Clark: A Master Cartographer