A master meter is a main meter installed ahead of a series of sub-meters. Master and sub-metering is common in tenant occupancies like office buildings, shopping centers, apartment complexes, and trailer parks. The master meter records all the usage to the facility while the sub-meters record only the usage of individual tenants or areas within the facility. This arrangement is desirable because each tenant’s usage is individually metered and can be separately billed. In most cases usage in the common areas is paid for by the complex operator, and this amount can be easily determined by subtracting the sub-meter amounts from the master meter reading. Master meters can be self-contained or instrument-rated depending on the power requirements of the customer.