An analysis instrument comprises plural modules connected together over a data network, each module comprising an analysis apparatus operable to perform biochemical analysis of a sample. Each module comprises a control unit that controls the operation of the analysis apparatus. The control units are addressable to select an arbitrary number of modules to operate as a cluster for performing a common biochemical analysis. The control units communicate over the data network, repeatedly during the performance of the common biochemical analysis, to determine the operation of the analysis apparatus of each module required to meet the global performance targets, on the basis of measures of performance derived from the output data produced by the modules. The arrangement of the instrument as modules interacting in this manner provides a scalable analysis instrument.