On-line balancing of mass and energy in a large-scale plant is today an absolutely feasible operation given the development state of the current data-acquisition systems. However, whilst the computing power is available. not all stream data are available in real-time and the programmed version of the instrumentation flow sheets in form of a graph cannot be used directly. They need to be modified so as to match the available information. Two cases are discussed: the dynamic case, where all units are seen as dynamic components and the steady-state case, where each unit is assumed to operate at steady-state. The analysis is done purely on a graph basis. The resulting algorithms are extremely simple and only require a depth-first path search algorithm. The idea is the essential part. Applying the algorithms yields simplified graphs, which contain in the dynamic case only computable quantities and the computation sequence. In the steady-state case one obtains a set of over-determined or dynamic nodes and a set of nodes that can be computed following sequence of computing computable unknown connections. (C) 2008 Elsevier Ltd. All rights reserved.