What is Water clock?
[[File:میراب زیبد گناباد.jpg|thumb|the show of old time keeping the tools called water clock by head of a [[qanat]] in Iran ]] A '''water clock''' was a tool for measuring [[time]] by the flow of [[liquid]] into or out of a vessel. Water clocks are one of the oldest time-measuring tools.<ref>{{Harvnb|Turner|1984|p=1}}</ref> The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in [[Babylon]], [[Ancient Egypt|Egypt]], and [[History of Iran#Classical antiquity|Persia]] around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks. == Designs == A water clock uses the flow of water to measure time. There are two types of water clocks: [[inflow]] and [[Outflow (hydrology)|outflow]]. In an outflow water clock, a [[container]] is filled with water, and the water is [[Drain|drained]] slowly out of the container. An inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines and tell how much time has passed. [[File:Water clock zibad.JPG|thumb|An inflow water clock in [[qanat]] Gonabad, zibad]] ==Regional development== ===Persia=== [[File:Ancient water clock used in qanat of gonabad 2500 years ago.JPG|thumb|Ancient Persian clock]] The simplest and more useable clock was a Persian water clock used by manager of the [[qanat]] . The use of water clocks in Persia or [[Greater Iran]] ,especially in desert area of [[Iran]] such as [[Yazd]], [[Isfahan]], and [[Gonabad]],dates back to 500 BC.<ref>{{cite web |first=G.H. |last=Rahimi |work=Tehran university science magazine |url=https://jihs.ut.ac.ir/article_69801_e14a6b2d0d61cd4df20e24ffd5b216a4.pdf |title=Water Sharing Management in Ancient Iran, with Special Reference to Pangān (cup) in Iran}} </ref> Later they were also used to say the exact time of holy days of pre-Islamic religions, such as telling the time of th