About: List of unusual units of measurement

An unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement, especially because its exact quantity may not be well known or because it may be an inconvenient multiple or fraction of a base unit. This definition is not exact since it includes units such as the week or the light-year, which are quite "usual" in the sense that they are often used, but can be "unusual" if taken out of their common context, as demonstrated by the furlong-firkin-fortnight (FFF) system of units.