 In some cases an owner of a mobile home park, apartment complex or commercial building may be billed by a utility based on the reading of one meter, with the costs shared among the tenants based on some sort of key (size of flat, number of inhabitants or by separately tracking the water consumption of each unit in what is called submetering).Displacement meters are commonly referred to as Positive Displacement, or "PD" meters.Two common types are oscillating piston meters and nutating disk meters.