The Lewis and Clark expedition utilized a number of navigational tools that were common in their day. Ascertaining latitude and longitude was accomplished using a sextant, and octant, a chronometer, and several types of artificial horizons. In addition to these instruments, the expedition carried a circumferentor, or surveying compass. The latter was utilized to find the difference between magnetic north and true north. While imperfect by the standards of today’s global positioning systems, they did allow the Corps of Discovery enough certainty to have a relatively good idea where they were at any given time. Nonetheless, a mistake of two degrees in calculations could mean an error of up to one hundred miles. Since they were in unknown parts anyway, this was not to provide a problem that could not be solved.
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