Editing Water clock (section)

===Babylon===
{{infobox artefact
|name = Clay tablet
|image =Water clock tablet.jpg
|image_caption =Water clock calculations by Nabû-apla-iddina.
|size = H:{{convert|8.2|cm|in|abbr=on}}<br />W:{{convert|11.8|cm|in|abbr=on}}<br />D:{{convert|2.5|cm|in|abbr=on}}
|writing = [[cuneiform]], [[Akkadian (language)|Akkadian]] 
|created = 600BC-500BC
|location = Room 55, [[British Museum]]
|id = {{British-Museum-db|29371|id=327283}}
}}
In Babylon, water clocks were of the outflow type and were cylindrical in shape. Use of the water clock as an aid to astronomical calculations dates back to the [[Old Babylonian Empire]] (''c.'' 2000 – ''c.'' 1600 BC).<ref>{{cite book | last = Pingree | first = David | author-link = David Pingree | editor = Stephanie Dalley |editor-link=Stephanie Dalley| title = The Legacy of Mesopotamia | year = 1998 | publisher = Oxford University Press | location = Oxford | isbn = 0-19-814946-8 | pages = 125–126 | chapter = Legacies in Astronomy and Celestial Omens}}</ref> While there are no surviving water clocks from the Mesopotamian region, most evidence of their existence comes from writings on [[clay tablet]]s. Two collections of tablets, for example, are the ''[[Enuma Anu Enlil]]'' (1600–1200 BC) and the ''[[MUL.APIN]]'' (7th century BC).<ref>{{cite book | last = Evans | first = James | title = The History and Practice of Ancient Astronomy | year = 1998 | publisher = Oxford University Press | location = Oxford | isbn = 0-19-509539-1 | page = 15}}</ref> In these tablets, water clocks are used for payment of the night and day watches (guards).{{sfn|Neugebauer|1947}}

These clocks were unique, as they did not have an indicator such as hands (as are typically used today) or grooved notches (as were used in Egypt). Instead, these clocks measured time "by the weight of water flowing from" it.<ref name=neugebauer>{{Harvnb|Neugebauer|1947|pp=39–40}}</ref> The volume was measured in capacity units called ''qa''. The weight, ''mana'' or [[Mina (unit)|mina]] (the Greek unit for about one pound), is the weight of water in a water clock.{{Citation needed|date=December 2020}}

In Babylonian times, time was measured with temporal hours. So, as seasons changed, so did the length of a day. "To define the length of a 'night watch' at the [[summer solstice]], one had to pour two mana of water into a cylindrical clepsydra; its emptying indicated the end of the watch. One-sixth of mana had to be added each succeeding half-month. At the [[equinox]], three mana had to be emptied in order to correspond to one watch, and four mana was emptied for each watch of the [[winter solstice|winter solstitial night]]."<ref name=neugebauer/>