What is Ruler?
[[File:Lineale.jpg|thumb|A variety of rulers.]] {{about|the measuring tool|the ruler of a country|Monarch}} A '''ruler''' (or 'rule') is an [[instrument]] of [[measure]]ment. Rulers measure [[length]]. Length is how long or short something is. Most rulers work by having [[number]]s (parallel<ref>Parallel means extending in the same direction.</ref> to the measuring edge) and little [[line]]s (perpendicular<ref>Perpendicular means at right angles.</ref> to the measuring edge). Rulers can also be used as a straight edge to draw lines with. Rulers come in many different forms. They can be made of [[plastic]], [[wood]] and [[metal]], and other materials. Rulers also come in a variety of lengths. For example, there are 1 [[metre]] rulers, 30 [[centimetre]] rulers, 20 centimetre rulers and 15 centimetre rulers. These are examples of [[metric system|metric]] rulers. You can also get 1 [[Yard (unit of length)|yard]] rulers, 18 [[inch]] rulers and 6 inch rulers, etc. These are examples of [[Imperial units|imperial]] rulers. ==Notes== {{reflist}} [[Category:Measuring tools]]