Digital signage is a form of electronic display that shows information, advertising and other messages. Digital signs (such as LCD, LED, and plasma displays, and projected images) can be found in public and private environments such as retail sto
In 1799 the kilogram was defined as the mass of a litre of water. In 1889, metal cylinders of the precise identical mass were created as reference objects.
In the hundreds of years since, the physical nature of the metal caused those cylinder