An accounting method and system is disclosed that provides for real time financial accounting of plant performance at a sub-plant level. A multiplicity of process variable transmitters is utilized to sense, in real time, the current state of the processes and process equipment used in a manufacturing plant. Sub-plant accounting modules utilize the sensed process data to calculate a plurality of sub-plant accounting measures, which are stored in one or more real time plant historian. The accounting measures are typically converted to a suitable format and subsequently stored in a production model accounting database where they are accessible to an accounting module.