An hourglass is a device used to measure time, typically consisting of two glass bulbs connected by a narrow neck. Sand or another granular material flows from the upper bulb to the lower one, marking the passage of time. The duration it takes for the sand to completely transfer can vary, allowing hourglasses to measure different time intervals. Hourglasses have been used since ancient times and are often associated with the concept of time itself. 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 of time management and the fleeting nature of time.