What is the primary purpose of a variometer in a glider?

The primary purpose of a variometer in a glider is to measure vertical speed, which is essential for understanding whether the glider is experiencing lift or sink. This instrument provides the pilot with real-time feedback on how quickly the glider is ascending or descending. By interpreting the variometer's readings, pilots can make informed decisions about where to fly in order to find the best lift conditions, enabling them to maximize their time in the air without relying on a tow or thermal.

In contrast, the other options do not align with the fundamental functions of a variometer. Measuring distance traveled is typically done with a GPS or a flight log device rather than a variometer. Monitoring wind speed does not fall within the variometer's capabilities; other instruments such as an anemometer would be used for that purpose. Finally, while battery life is crucial for powered aircraft, it is not relevant to a variometer in gliding contexts, as the instrument's focus is solely on vertical movement. Thus, understanding lift and sink through the use of a variometer is vital for effective gliding.