Assertion: celestial navigation | /r/Desires | marine chronometer
Facets:
value: usually
type: TEMPORAL
value: to measure time
type: PURPOSE
Source sentences:
text: Practical celestial navigation usually requires a marine chronometer to measure time, a sextant to measure the angles, an almanac giving schedules of the coordinates of celestial objects, a set of sight reduction tables to help perform the height and azimuth computations, and a chart of the region.