The Anglo-Saxon system of units is a collection of measurement units distinct from the metric system, which is currently used as the primary unit of measurement in the United States, the United Kingdom (formerly), and some other countries and territories connected to these two, such as Puerto Rico, a Commonwealth of the United States. There are several differences between the systems in the United States and the United Kingdom, where it is known as the imperial system, as well as regarding the disparity between past and present values.