Which of the following describes the nature of a sextant?

A sextant is a precision instrument used in celestial navigation, allowing navigators to measure the angle between a celestial object and the horizon. This ability enables sailors and aviators to determine their position at sea or in the air by calculating their latitude and longitude based on these angular measurements. The design of the sextant involves a movable arm (the index arm) that allows for precise adjustments, making it possible to obtain accurate readings.

This instrument is an essential tool in navigation, particularly before the advent of modern GPS technology, as it provides a means to navigate based on celestial bodies such as the sun, moon, planets, and stars. The reliability and accuracy of the sextant in measuring angles are what make it a fundamental instrument in maritime and aerial navigation.

The other options do not accurately describe the sextant's capabilities; it is not used for navigation by sound, it is suitable for use both at sea and in the air rather than just on land, and it does not function to measure wind speed, which is a separate aspect of navigation and meteorology.