An hourglass is a device used to measure time, consisting of two glass bulbs connected by a narrow neck. Sand or another granular material flows from the upper bulb to the lower one, taking a specific amount of time to do so. The duration can vary, with common hourglasses measuring intervals of one minute, five minutes, or even longer. Hourglasses have been used since ancient times and are often associated with the passage of time. They are sometimes used in games, such as chess, to limit the time players have to make their moves. The design of an hourglass is simple yet effective, making it a popular symbol for time management and the fleeting nature of time itself.