Penny Napoleonic Wars prompted the use of base metals in 1797. Despite the decimalization of currencies in the United States and, later, throughout the British Commonwealth, the name remains in informal use. No penny is currently formally subdivided, although farthings (¼ d.), halfpennies, and half cents have previously been minted and the mill (1/10¢) remains in use as a unit of account in some contexts. "Penny" is first attested in a 1394 Scots text, a variant of Old English ', a development of numerous variations including ', ', and '. The etymology of the term "penny" is uncertain, although cognates are
Penny graph are the coin graphs formed from unit circles. If each vertex is represented by a point the center of its circle, then two vertices will be adjacent if and only if their distance is the minimum distance among all pairs of points. Therefore, penny graphs have also been called minimum-distance graphs, smallest-distance graphs, or closest-pairs graphs. Similarly, in a mutual nearest neighbor graph that links pairs of points in the plane that are each other's nearest neighbors, each connected component is a penny graph, although edges in different components may have different lengths. Every penny graph is a unit disk