Instead of using N-1 separate meters, the meters are combined into a single housing for commercial purposes such as measuring energy delivered to homes and businesses. Each pairing of a current measuring unit plus a potential measuring unit is then termed a stator or element. Thus, for example, a meter for a four wire service will include three elements. Blondel's Theorem simplifies the work of an electrical utility worker by specifying that an N wire service will be correctly measured by a N-1 element meter. Unfortunately, confusion arises for such workers due to the existence of meters that don't contain tidy pairings of single potential measuring units with single current measuring units. For example, a meter was previously used for four wire services containing two potential coils and three current coils and called a 2.5 element meter.