What does a chronometer primarily measure?

Explanation

A chronometer is an instrument designed for highly accurate time measurement. It is engineered to maintain precision despite changes in environmental factors like temperature and humidity, making it essential for precise timekeeping, especially in maritime navigation. Historically, chronometers enabled sailors to determine their longitude by comparing the local time with a reference time. To earn the title of chronometer, a timepiece must undergo strict testing to verify its accuracy under various conditions.