What is Paley's watch analogy?

Paley imagines someone finding both a watch and a stone. Unlike the stone, it would be obvious that the watch did not get there by chance as it shows such evident signs of design. He believes the watch must therefore have a designer. Paley draws an anaolgy (a comparison) between the watch and the universe as the universe is much more like the watch. The univesrse shows elements of designs and could not have happened by chance and so it needs a divine designer. He furthers the analogy by stating that if there are parts of the watch/universe that do not work the anaology is not weakened as both still show evidence of design. The purpose of the analogy is to prove God's existence through comparing his nature as a designer to something that humans can understand, anaolgies give clarification and make arguments more compelling as they become relatable.