Cách sử dụng
An hourglass is a device used to measure time. It's shaped like two glass bulbs that are connected with a skinny middle part. Sand is poured into the top bulb, and as it falls through the skinny part into the bottom bulb, it measures a specific amount of time, usually an hour. The hourglass was used a long time ago before we had clocks and watches. Nowadays, people might use an hourglass as a decoration, in a board game, or in a workout routine.