Sundials have their origin in shadow clocks, which were the first devices used for measuring the parts of a day. The oldest known shadow clock is from Egypt, constructed about 3500 BC, are also among the earliest shadow clocks.
An hourglass (sandglass , sand timer , sand clock , egg timer) measures the passage of a few minutes or an hour of time. It has two connected vertical glass bulbs allowing a regulated trickle of material from the top to the bottom. Once the top bulb is empty, it can be inverted to begin timing again.