What instrument is used to provide the height of a balloon above sea level?

The instrument used to determine the height of a balloon above sea level is an altimeter. An altimeter works by measuring the atmospheric pressure, which decreases as altitude increases. This pressure change can be translated into a height above sea level, enabling the altimeter to provide an accurate reading of altitude.

In the context of ballooning, where altitude can vary significantly, the altimeter is crucial for pilots to monitor their flight level and ensure safety. It gives real-time feedback on altitude changes, which is essential during ascent and descent.

Other instruments may be involved in atmospheric measurements (for instance, a barometer also measures pressure but does not specifically indicate altitude), but the key characteristic of the altimeter is its calibration and design specifically to convert pressure readings into altitude measurements. This precision makes it the instrument of choice for understanding and managing flight altitude in aviation and ballooning contexts.