A sand timer, also known as an hourglass, is a device used to measure the passage of time. It consists of two glass bulbs connected by a narrow neck, allowing sand to flow from the upper bulb to the lower one. The amount of sand and the size of the neck determine how long the timer runs, typically ranging from a few seconds to several hours. Sand timers have been used for centuries in various cultures and are often associated with timekeeping and navigation. They are simple yet effective, providing a visual representation of time passing. While modern clocks and timers are more precise, sand timers remain popular for their aesthetic appeal and simplicity.